Many locals seem to buy most of their day to day building and home improvement items from IQ in Surin. Far superior than all of the local little builders merchants. But even with the discounts given to many farangs, it is still rather expensive.
Came across "DO" on the outskirts of Korat last week (Just a bit further up on the right from Dan Kwian on the road into Korat), An enormous warehouse outlet, with a huge selection of virtually everything, some at ridiculously low prices, and most far cheaper than Surin.
Well worth a visit, but avoid weekends and try and get there as near to 8am opening as possible.