Even in Thessalonica, you sent me help for my needs once and again. Not that I seek the gift, but I seek the fruit that increases to your credit. I have received full payment, and more. I am well supplied, having received from Epaphroditus the gifts you sent, a fragrant offering, a sacrifice acceptable and pleasing to God. (Philippians 4:16-18)

Giving is never easy. Supporting missionaries and their work is sacrificial. This means it takes a real decision to give rather than not give. You could do something else with the money! Yet as the apostle states above, we seek the FRUIT that comes from the work allowed by ones gift. 

That FRUIT is counted toward the giver as well as the  preacher/evangelist/missionary. God regards the giver as a partner in ministry and so do the workers in the field, trust me on this. Those who cheerfully support the spreading of the Good News are a vital part of the ministry. 

If you cannot GO, then GIVE. 

If you cannot GIVE, then PRAY for God to cause others to GIVE! Join God at work!