I have a Tag with a diamond dial I paid over 12,000.00 for on resell I would expect about 1/3 that. So if cost was 200 then you might sell it for 50-75.
If you don't remember how much you paid in-store, then I would take it to be valued. Say it's worth £8,000. Sell it for about £7,250 or so. Good luck!
OMG! I could have had one for free! I should have snagged it!
Id say £100-£500! How much did you buy it for?