I had a similar experience - went to buy some timber and found they wanted to charge three times the price that I knew B&Q were selling the same timber for (9 miles away)
I asked them to price match, and the chap didn't bat an eyelid and just keyed in a 65% discount for me.
I'm about to spend 2k on materials (blocks, sand, lintels, etc) and wonder how to go about it - attempt to open self build or fake trade accounts and see who gives me the most discount, or just be honest about it and get comparative quotes and see who quotes the lowest price.
Gary