$24.99 or around £12 is a fair price .
Your focusing on the name TWIGGY more than the pantyhose , the devils is in the detail also which could push the price up, a friend of mine sold on Ebay a pair of 60's pantyhose in the UK for £30.00 ($62) nothing special brand wise but they wear fully fashioned .
If they are 100% nylon, or fully fashioned or with a real seam then that could push the price up on a good day.