It's nice to see another owner in the UK.
I imagine it would depend on how accessable your supplies are. Can you buy them from a local shop or do you order on line? I can't see why having one more would be that much more expensive. You have the initial costs of a cage and toys but then after that if you are buying the food, hay, dust etc anyway you aren't going to use that much more.
I only have one so I can't tell you for sure.