There is a very active Yahoo group called homequiltingsystems that would be a good source of information for you. Check their "files" section; lots of comparison info about midarms and longarms, and some pricing info on different types of setups. Posters have everything from very basic systems to professional setups.
The rule-of-thumb advice from that group is to research for a year before purchasing. That would be a good time-frame for your weight loss too!