Seem to go for £20 - £30 on ebay. Perhaps on a forum you could get £20 each but there is no depends if anyone will want them.
On ebay maybe £25 each I might try. £30 is too high I feel, £15 too low with the fees and delivery and all that.
Hope that helps, it is hard to price used PC parts and can be very hard to get rid of which is why I never buy the best gear, you can give it away a few years down the line.