Agreed on the Tarptent brand. Good value, watch for sales. Check into BackpackingLight.com forums. Also look into small tent + tarp. You can set outside under the tarp in crappy weather, cook, etc, and drop it over your gear at night. Are mosquitos going to be a problem? Light and cheap, pick one. 4 lbs all-up packed weigh is moderate, more than that becomes heavy. Are you going to be touring where you can put stakes down or use heavy rocks, if not you need a freestanding tent. I am looking to replace my 6 lb all up tent, either with a ultra light one person or a hammock.

I really prefer REI for their warrenties, but they are not in the ultralight realm. I think Eureka has some moderate weight one man tents in the sub $100 range. Wish I had some specific recommendations, but if you post links to what you are looking at we can give you critical feedback.