Considering the budget and your needs, I'd recommend looking at the SD Baku 1. Campsaver still has them at 40% off and it's even lighter at 3.5 lbs packed weight...$138. The rainfly is integrated, but there's plenty of surface area that can be zipped open to allow good airflow in the summer. Plus the vestibule is huge for a single sleeper.

http://www.campsaver.com/Itemdesc.asp?ic=sid0075