Sorry that I didn't see this sooner.
Actually, you're not asking for too much at all. Not for $150 or less. This
is easily the most powerful card that your PSU can handle. It's quite a bit faster than either of those other cards that you linked to and it's within your budget. You can get an additional 2% off if you have a Windows Live ID and go to Newegg via Bing Shopping, making the final price $117.29.
EDIT: I'll keep you up to date when I find new deals if you want. I may be able to find a 1GB model for not much more if you want a bigger frame buffer. The 5770 is definitely the
card to get in your price range that will run on your power supply.