"Im genuinely intending to sell them, just need to fix a price. I looked on Ebay.co.uk but there are none there."

I would think that if you put them on eBay with no reserve you will get a fair, and pretty good price. I think there are quite a few of us apprehensive about what we will do if one of these filters needs replacing, and would pay for the peace of mind of having spares ro hand.
Richard