Provided his travel cage is either a hard-sided carrier, a wire-top plastic bottom cage, or other cat-proof "home," he should be okay at your aunt's for one night.
For now, if you and hedgie are stuck at home with no a/c, a couple make-shift ideas to make a cooler spot for him:
- use something that transfers heat away from his little hedgie body - like have him snooze on top of a plate instead of fleece
- make sure he has plenty of water to drink
- cool a small area of his home using freezer packs/frozen veggies/ice cubes in something waterproof (bottle/ziplock) stuffed in a sock so he can't get at the plastic/frozen parts directly
- put his cage on the floor instead of a table/desk/whatever it's on
- if you have a car with a/c, take a small trip with him to somewhere safe and air conditioned
General idea: if it's too hot for you to stay in the house, it's going to be too hot for him. 80's stink, 90s are bad, if you're hitting 100 in your house and you can't stand it and need to leave, you can be sure he won't fare so well either.