Maternity Leggings??!

Helppppp!! I'm not huge yet, but I want to be prepared as I progress through my pregnancy. I'm not having any problem with tops, but it seems impossible to find good quality maternity leggings (for working out, not just everyday wear) at reasonable prices.

I'm a fitness instructor so these are my "work clothes" and I don't want really thin pairs you can see through or tear easily, but I also can't afford to spend an arm and a leg because I would like to have two or three decent pairs so I'm not doing laundry every single night.

I'm going to try the old navy ones, but that's about all I've found in my price range.

Any brands anyone can recommend?