I don't really know of any under $100. I know that several people have made their own using pvc & plastic hardware clothe (& zip ties), possibly for that amount or less. A lot of people prefer those, but I'm not personally sure about them in the long haul, though you can do a lot with them for size and personalization.
You can search on ebay, I have seen cages there for maybe that price range that look okay, but they are sized a little smaller I believe.
Hopefully someone can offer you more help or perhaps you can link some you are looking at and get opinions on them.
I have personally only purchased HQ cages and I know of several that use the CNC or ALT (PetSmart) cages.