Here's a brief overview of what to look for in a jigsaw
http://direct.tesco.com/buyersguide/power%20jigsaw.aspx
If you're on a budget, go with what you can get. Read reviews online, such as amazon, or some shop magazines that review tools, and maybe even a consumer report website (you might need to pay though). If you hate the tool, you can return it because some tool stores have great return policies.
My mom bought a jobmate drill, because maybe at least once a year she needs to use it. It's not the best drill, I would never take it on the jobsite, but to drill a few holes why not? Driving with it sucks. Sometimes its not so much the tool, just the tool who's using it