Here is a $30 single-wall tent with built-in floor and mosquito netting, that is a bit small, though perhaps usable, for two people.

http://www.campmor.com/outdoor/gear/Product___35842

If you substitute sticks for included poles and stakes, it's under 3 pounds. With the included poles & stakes, it's 3 1/2 pounds.

A tent like this is utilitarian in three seasons. It's simply all you need and works totally fine if seams are correctly sealed. I used something like it in a heavy wet snowstorm, and was innundated with condensation and also melt-water from snow slopped into the tent. Partly, this was due to waterproof floor holding water rather than permitting it to drain into the snowpack.