I buy most of our clothes at a consignment store. She only takes the very best of clothes, in fashion and in good style, they have to be fresh washed and pressed, stain free and near perfect. I usually pay $3.00 - $5.75 for a matching outfit fromPenneys. You know the ones, pants and a coordinating shirt. You might find a local store and check out their prices to be able to price your items similarily. I find them to usually be very affordable. Like a one peice sleeper for a couple of dollars. I find the little girl frillyparty dresses are usually for sale there for about $8.00 to $15.00. Most of those go for $50.00 and way up brand new. This way you can get a guideline for what the going rates are in your area and tell your friends that's how you'll price the items.
But if it comes down to it I'd say good friends are more important than money so take into consideration if they can afford to pay very much. If their money is tight you can see what the prices are in the consignment store and maybe make your prices a percentage lower than that. For example, if they had a little boys suit for $10.00 and I had one very similar and was going to sell it to "Mary" but Mary's husband may be out of a job soon and they are really pinching pennies, then I might price it 20% less for $8.00 just for her.
My friends and I have found that clothing exchanges work well for us. We bring everything we want to get rid of once a year in the Spring and again in the Fall. We put stuff on tables in the Cultural Hall at Church by size and gender and we take whatever we want. If anything is left over we can take our items and take them with us or we can put them in a pile that someone will take and donate to a needy family at Church or if no one needs anything we take it to a local agency that gives clothes away for free to needy families, like a clothing closet.