Yep I too managed to pick up a couple of items including a new alternator for £50 (believed to be a good deal at the time). Lawrence, bless him, was the master of buying technique and taught me plenty whilst there. Was also kind enough not to laugh at my mistakes too.
Take a wad of cash, check out what you are after across different sellers, and pitch up to buy as near to end of the show as you dare...that's where the bargains are to be had, I believe
And remember ... in todays' plastic money society, cash remains the best way to ensure rock bottom pricing at this kind of gig!