Unless you can find one used, then you probably won't find a decent cage for "fairly cheap". I had a cage from Petsmart as a starter cage; it came as a kit and cost $90. I upgraded to a Critter Nation, double unit ($250) that I ordered from Amazon. (The starter cage would have been sufficient, but I was supposed to get another chin; I had planned to upgrade regardless though so my boy would have a lot more room)
Are you just looking to use something temporarily, or permanent? If permanent, remember that chinchillas have a pretty long lifespan, so in the long run investing in a better cage doesn't cost all that much.
If finances are tight, then I see people post about cages on Craigslist so you might be able to find a decent one used somewhat local to you. Good luck!