One option would be for you to spend the money on a POD or something like that. If you play live, you could just run direct to the PA and make use of it that way. Once you get the Mesa, the POD will still be an invaluable tool for use in recording and practicing, plus it's portable and can go with you just about anywhere. You obviously have a computer and the POD would be great to plug into your soundcard and record with, get ideas down or work on soloing over that tricky chord progression. I've got a mesa but I use my POD Pro every single day for practicing and what not. I'll never get rid of it, it is a great tool to have at my disposal and it sounds fantastic. I only use the mesa for gigs, in between all my work is done on the POD Pro. Simple and effective for my needs.
If you dump the cash on another cheap amp, once you get the mesa you're left with a cheap amp you can't really use anymore...it doesn't provide you with any real value. Just another perspective.