Remember that God is our provider, not people, though He works through people. Trusting Him to supply for your mission trip is a spiritual adventure of faith. Consider it part of your growth and faith journey that you go through in preparation for the task ahead.
The basic principle that you need to understand is that people are giving to God (His work) and not to you personally. You need to have a sense of purpose when you ask and there is no greater purpose that God’s will or the Lord’s work. Do you have a vision or idea of how the Lord may use you? Do you have a vision of what He may accomplish in your life and those around you as a result of this trip? I don’t need to tell you that God desires for all to enter His Kingdom, for every person to have one chance to hear about His waiting forgiveness. If you do anything that helps lead one person one step closer to Christ while on your trip, then you are doing the greatest work on Earth.
First thing you should consider are the financial sacrifices you can make before asking others to make them with you. If you find that you still simply cannot afford to take this step without assistance, then you must take a spiritual leap of faith and trust that the financial means will ultimately be provided. Of course, faith and trust in God do not imply that you are to sit back and wait for money and cheques to come to you. You still have the responsibility to be proactive in providing opportunities for others to financially share in your mission.
It is good to give. The first contribution toward your cause should be your own. Don’t worry, you don’t have to give until it hurts or cash in all of your savings.
Your financial gift helps you in many ways. First, in addition to you going and investing your time, it provides you away to give to the Lord. Second, it helps you commit yourself to the task. Third, it helps you not to feel as though all you are doing is taking. Firth, it sets a standard by which you are going to trust the Lord for His provision.