I don't think you'll be able to get $50 for them loose without clothes.
Do any of them have bangs? If not, and if they don't have their clothes, I don't think they're worth much because they've been produced so many times.
Although Twilight might be worth a little more? Since she's a unicorn, and all future toys of her will be alicorns? Just speculation on my part, I don't know for sure.