Cheapo tents are just fine for weather that's just fine. Art's right that construction has gotten better. Flys and seams and floors come into play big time as the conditions worsen. An easy solultion if you get caught out in it is to make sure you use a ground sheet, and then cover the works up with a well secured tarp. Ventilation might be a problem but you'll survive. Also, if the tent has a bathtub floor, it does help a alot.

Remember, the better you take care of your tent, tne better it will take care of you.