Should i buy anthor horse or should i rent one like a school horse?

i own a 4 month old Colt my baby boy but any way i cant ride him or anything for quite a while and i want to learn more in the riding dep . because of age and i was wondering what i should do and id want to buy a mare if i bought one .also what would it cost to rent or lease a horse and basic cles i live in mt we live in the south west Conner of the state,