I popped into Lidl yesterday and they had a great choice of seeds.
The display stand was so full that I got the impression that it had just gone up, as it was jam packed with seed packets.
The prices range from 29p a pack - brilliant value. The cheap packs often seem to have a lower number of seeds (I bought melon seeds and there are 30 in the packet) but unless you have a massive garden or allotment the small quantities can be just right. In case anyone's wondering, I'm not on commission, just really pleased with the bargains I picked up there.
I've also saved a few seeds from a pepper - even cheaper! Not sure if they will produce true to form peppers (they might even be sterile?), but will give them a chance.