Wow, that's a hefty price on Discogs. I paid £2 for mine, yesterday. I had no idea that some cassettes might still be collectable, Ever since I moved house, a few months ago, I've been planning to take a boxful down to a local charity shop but perhaps I need to have a look through and check whether any of them are worth a few quid!
Drop me a line...I'm a collector. I'll (almost certainly) promise not to lie...

Will do. Though I should imagine most of them won't be of any interest, there might be a few that might be up your street. I'll send you the list tomorrow.