don't skimp.

some of those single wall shelters suck for ventilation.

do your research,
i strongly reccomend buying a copy of Backpacker Magazine's annual GEAR GUIDE, or reading it at your public library.

and regardless of what tent you buy, pick up a lightweight silicone coated tarp to use as a bike cover, cooking/cover the picnic table shelter. very, very handy.

i personally like just tarps for everything except extreme bugs and/or KOA type campgrounds.