Depends very much on condition, scarcity and whether or not they ever made it onto CD or "iTunes". You can usually get an idea of what a record is worth if someone is selling it on eBay. Christy Moore's very first record, "Paddy On The Road" sold 2 weeks ago for £256, and the guy selling it had had an asking price before that of £600 ! There's a new vinyl shop opened here in Aberdeen a few months back. The LPs in their "folk" section vary from £5.00 - £20 last time I looked.
Oxfam did used to have a specialist music collector's website a couple of years ago, which if it still exists, I'm sure they'd be delighted to accept any records you'd be prepared to donate to them.