Do you have schools near you to share music with? Other music teachers would have pieces that they know work and they would most likely be happy to share if they know you will return all copies or replace any that are lost. I am not aware of rentals for choral music as most choral music costs $1.95 to $2.50 a copy paying rental on each piece would be a waste of money. Use your resources to purchase a couple of really good titles a year and build up your existing library.
Chair, NAfME Choral Education Council Chair