Is this cage one you want as a temporary cage till you get these two to be friends or is it one you want them to live in once they are together?
All my chin and degu cages are metal with solid metal bases. Personally with chins from what i have read solid metal bases are better then plastic because chins gnaw and they are good at it and can easily get through a plastic based cage (i know this from experience with degus is definately true) and also if they ingest plastic it can cause serious problems so metal bases are always a good choice. As to what size it depends on if this is a cage for the two or just a temporary one till you get them together?
I'm not from the US but i know people rave about Martins Cages and they do cages for chins. They are simular to the cages my degus are in and i've never had any problems with this kind of cage. With chins the only thing i would do is remove the metal shelves and replace them with solid wooden ones as they are much better for the feet
www.martinscages.com
If they are out of your price range as i noticed you said you wanted something cheap the site might still give you some ideas and maybe you could make your own or look for a simular cage. Have you tried ebay? Lots of bargains to be had on there, my friend recently got a brand new cage for half the price of anywhere else she had tried and that included the P&P
