Yes the ones with different covers tend to sell well nowadays. I wanted a couple of them but was too pricey for me.Someone sold about ten really interesting ones last week. I didn't bid on any as I had most of them and then 4 that I did want were all at 60/70 quid by the first day or so.
Cassettes have really gone up in price rapidly the last three or four years.
It was only a few years ago that i was picking up most of my cassettes for £10-20. Then a couple of years ago it was £30-49 and now it seems to be £50+ for anything interesting.