Split it up, price everything according to quality, take about two, three dollars off of each price for it having been used, or however much you like, and then add it all up. Easiest way to get what it's worth.
That depends on how good of shape they are in, and if you paid a lot for them. If they are in great shape, and you paid a good bit for them...I would say $80.
However, if they are in good shape and you got them free, or from a thrift store...I would say $50.
If they have holes, stains or anything like that...and you got them free or at a thrift store, I would say $20.
I think that $50 - $60 is a pretty good price range personally. It's unfortunate, but these days, you can't really get much more. Here, usually prices go as low as $40 for a whole box of items.
In any case, if you'd like to get more, I suppose you could try posting the ad with a higher price, saying that you're willing to negotiate? If you're fine with $50 - $60, though, definitely go for it.
Take a look and see the prices other people are asking for a similar amount of clothes. That will give you a good price range. Try to always go ten higher then what you want and then offer the buyer less when they come to look at the clothes. You will be getting them for the orice you want and they will think they are getting a deal. Everyone will be happy!