For kids clothing, unless you are in a major metro area, I expect to pay $0.50 to $1. Maternity you can ask $2-$3 if they are long sleeves, pants, etc. Otherwise $1 for tank tops or things like solid color, short sleeve T's.
Men's and women's clothing are very hard to sell usually. The toughest thing.
Men's dress shirts might go for $2 each if they are great condition. I'd charge $0.50 a piece OR a per bag price. Say, everything you can fit in a bag for $4.00.