Paul clearly was one of the first or best known of the New Testament missionaries. What most people do not understand or realize is that the term "apostle" comes from a verb meaning to send on a mission to accomplish, getting that person the authority to represent and the wherewithal to perform the task. This corresponds to our modern concept of "missionary". Few would dispute the fact that Paul was a missionary. This was his primary and principal job. Anything else he did was incidental to his being a missionary.
In 1 Corinthians 9, Paul puts forth his defense of his ministry as a missionary ("apostle"). The context is that Paul founded the church in Corinth, and after having founded this church, false teachers moved in and turned the church against Paul, probably during the same time that he was establishing it. Paul did not get support from this church, but Paul's teaching is that the Corinthian church clearly had a biblical obligation to support him because of his preaching and teaching ministry among them.
2 Corinthians 11:8 I robbed other churches, taking wages of them, to do you service.
Here Paul describes his situation with the Corinthian church, making note of the fact that because of their unspiritual, carnal attitude, their being babies in the Lord, Paul refused or passed over taking recompense from them, but clearly they had that obligation towards him. In stark contrast to the Corinthians, the Philippi church supported Paul from the outside of his ministry, and Paul appreciates them for this.
1 Corinthians 9:10 Or saith he it altogether for our sakes? For our sakes, no doubt, this is written: that he that ploweth should plow in hope; and that he that thresheth in hope should be partaker of his hope. 11 If we have sown unto you spiritual things, is it a great thing if we shall reap your carnal things?
God's principle is that the worker who works a field has a right to receive of the fruit of that field. Involved in this principle is the point that according to the dynamics of the situation, (1) how well the field is prepared, (2) how good is the ground, (3) how well the worker works, (4) how God blesses that field, that crop, that year, etc. these are the things that decide how is the yield, and these are things that would affect how much the worker would receive. The steward that is over a field that yields very little, he himself gets a minimum acceptable salary. But the worker that puts in extra effort, likewise will see a recompense that corresponds or reflects that extra effort.
1 Timothy 5:17 Let the elders that rule well be counted worthy of double honour, especially they who labour in the word and doctrine 18 For the scripture saith, Thou shalt not muzzle the ox that treadeth out the corn. And, The labourer is worthy of his reward.
God's principle is that a worker should receive of the fruit of his labors, and "double honour" in the context of preaching and teaching. The principle that a laborer is worthy of his reward means that according to the labors of a person, so should their recompense be considered.
How much should a minister be paid?
1 Timothy 5:18 For the scripture saith, Thou shalt not muzzle the ox that treadeth out the corn. And, The labourer is worthy of his reward.
Matthew 10:10 Nor scrip for your journey, neither two coats, neither shoes, nor yet staves: for the workman is worthy of his meat.
Luke 10:7 And in the same house remain, eating and drinking such things as they give: for the labourer is worthy of his hire. Go not from house to house.
From these passages, we see more support for the paying of ministers a just salary for their labors. In Matthew 10 and Luke 10, we note that the context of these passages is that Jesus sent out his disciples to minister as short term missionaries. Very simply, they raised no money, but they lived by faith. Apparently one of the basic or foundational teachings of the early church was something to the effect that the minister should be supported by those he ministers to. This is a rule. Therefore, the people that receive the direct teaching and preaching of that minister should financially support him. This is a principle that should not be passed over lightly. The only exception to this principle is that of missionaries, and yet we see very clearly that Paul taught this principle even so among the churches he established.
As an aside, we study Paul's ministry, and we note that the church in Antioch sent Paul and his group out (literally they divorced themselves or fully cut themselves off from having any further dealings or obligations with Paul). When Paul mentions the faithfulness of the Philippian church in giving since the beginning of his ministry (Phil. 4:15), they regularly gave to Paul as they had opportunity (somebody passed through their church going to Paul that could take a donation to him). This means that the church in Antioch apparently did not regularly send money to Paul. Indeed we have no record of them ever giving to Paul. Perhaps they did, but the Scriptures do not mention or record it.
Therefore the mention of this financial obligation must have been very quickly after the disciple saw saving faith in the person he was evangelizing. Very definitely three points come to bear here on these verses: (1) begging is not part of the plan of God in world evangelization, (2) those very people who accept the gospel are quickly supposed to be taught and start corresponding in kind or in payment with the minister of the gospel, and (3) there is a donation by established churches towards the ministers that are "on the front lines", the missionaries. These ministers are the people who are evangelizing the lost, and organizing them in local churches, and establishing these churches. No other kind of missionary ministry is seen in the New Testament. Medical missions was first evangelists and church planters, then as the opportunity presented itself, they did medical work. Most medical missions have that backwards, they present medical help as their primary ministry, and they witness and very, very seldom plant churches as an add on if they have time. We see no other kind of ministry among the missionaries (those supported by distant churches). We also see that all of the charitable type ministries were local in character as a ministry of the members of that local church to local people in need. This means that they were not supported in respect to salaries, and their labors and time was voluntary, not a full time job.