Did you really come right out and ask them to buy a keyboard? When you did or do ask, did/do you have a list of possible boards and their prices? It is totally unreasonable to expect a person to haul and use their own equipment to play and not be paid anything. (unless they just want to do it)
Sometimes, though, if nothing is said, people might think that you are satisfied doing it as a donation to the church. Some might not even know that you are not being paid.
You can get one of several acceptable to good keyboards for less than $500.00. This amount is well within the reach of almost any church. A big church might want a more expensive and comprehensive board.
If they knew your concern(which is very reasonable)it would seem very unlikely that they wouldn't act. If they don't, the decision to be made is yours. In any case, not an easy one.
berbie