Milky, you've missed the point. You were protesting about the cost of decent 5 GTT's going up and ruining it for everyone. But the reason for the increase is normal market economics. Supply of GTTs is low and demand for them is high, so the price rises. Who can be blamed for this?
You seem to be aware of the affect supply and demand should be having on the decals you have for sale however, due to their scarcity. So if we take this as a case in point, I'd imagine they were less than £20 when new. Seeing as the run-out GTT's were circa £10k and a fine example can currently be acquired for around £5k, then maybe the price of your decals could be around the same '50% of new price' marker, at a tenner?