Are your bars to big? You could try to do an exchange with were you got cage at?
but if your bars are 1/2 inch apart or about 12mm you should be ok.
one other option, not the best, is I can get plastic chicken wire at the local hardware store, buy some tie wraps and tie the chicken wire around the cage. This isn't the best, if he tries to get out he could get stuck between cage bars and chicken wire, you would have to tie wrap in up really good.
I have a picture in my picture files that show the playroom made of chicken wire.
this would cost you maybe $50 verse $225 for a new cage.