Small cages like the 25" Ware Chew Proof Small Animal Cage and the Kaytee My First Rat cage would do the trick. You may be able to find similarly sized used cages. If it's just temporary, your rats will be fine in a smaller 2 to 5 cubic foot cage.
I think a bin cage is great. There are ways to make a totally chew-proof bin cage. First, you want to select a bin that is very square on the inside without ridges or edges that your rats can get their teeth around. Then, if you attach the hardware cloth to the inside of the windows, your rats won't be able to get their teeth around the openings to enlarge them.
Making a [
bin cage] is really cost effective but it's a little bit of work and may require a couple basic tools. Another nice thing about a bin cage is it can be used as storage when it's not being used as a cage.
A temporary cage doesn't need to be huge but also think about other possible uses. Besides during quarantine/introductions, a secondary cage will come in handy if you need to travel with your rats, as a hospital cage, or just as a safe place to put your rats when cleaning their main cage. When figuring out what you want to do, think about these other uses and make sure they will be met, as well.