I wash mine whenever I see mold starting. At most every 3 months.
I don't pay much for them either but I can't see sending a big, plastic tarp to the landfill all the time. I buy whatever is between the cheapest and the most expensive and they hold up very well in the wash.
EveryNameIWantIsTaken:We rarely wash ours, but it never seems to get gross looking either. It's made out of some sort of fabric though, not the vinyl, but it still doesn't let water out.
This. I made sure to buy a nice one that is washable. I've had the one in my guest bathroom for six years and it still looks great. That shower does not get used much so I wash it every six months or before guests come visit.
I don't. I buy them at the Dollar store and just throw them out when they start looking yucky. They are very thin but I don't care - I've never had a problem with leaking or tearing and it's much easier than having to wash them.
I tried washing one of the expensive ones and it came out funky.