In reply to fionafluffy: We ahave a gore exchange light one, its a nylon base for cheapness i guess and a gore top. the fabric is air permeable so you can zip yourself fully inside quite happily and so it doesn't need a pole/vent/complications.
Ideal for minor weather issues and I've been really impressed
not sure on cheapness, i got it from CCC/Go outdoors on some sort of deal.
ALternatively my friend has a tarp tent which is both very light and cheap. an american concept that seems to work well. it's roomy one person thing as you can't touch the walls and relies on ventilation to keep condensation at bay. I was really impressed, friend got it online she's alexD on here so may send you a link or soemthing if you ask.