Craigslist is one of the better places.
Sadly, you can recoup some of the cost but honestly not as much as most people wish......each dress will probably get $2-3, maybe $5 if in excellent condition. If you put it all together and ask $20-25 you might do better.
Once Upon a Child stanards are so subjective. I had an extremely gently used shoes and one girl said the style was dated, another girl offered $4. for them.....the manager had to get involved to settle it. Some of the ones who process the clothes act like their are close to God.....judging what can sell and what they don't want.
If you get a good processor, as I often have, I walk out with a check for about $40 and a lot of clothes that I thought they would take and didn't, so I take them back with me.
Good luck and keep us posted.