Are mini-fridges and/or microwaves available to rent through student housing? Or do you have to purchase?

They are not available. However, are common fridges and microwaves for everyone to use in every dorm. If you want your own in your dorm room, then yes, you would have to purchase them.

How much is it to rent a mini fridge?

You can rent a fridge through RPI’s vendor. That being said, a mini fridge by itself to rent is $120 and a mini fridge with a microwave on top is $220. The cost to purchase a standard mini fridge at Walmart is $90-120 and the cost to purchase a microwave is $60. In total, that would be about $180 and you would own the two items instead of renting for $220 and only for a year.