What's your actual budget? People sometimes have very different ideas about what "budget" really means! I'm not sure I'd recommend it as such, but something like this CIT would probably do the job:
http://www.ebuyer.com/247132-cit-s00...psu-cscits003b
The biggest issue with a nice small mATX case is that a lot of them have non-standard PSUs built in, and you can never be sure of the quality of PSU that you're getting - unless you're willing to spend a significant amount on the case and PSU together, anyway....