It really is mostly about the land value, with a bit of local planning opposition. Allowing people to build un-code houses would save a surprisingly small amount of money in the short term at the cost of all sorts of long-term problems.

In the UK if you want a house but are completely agnostic about where, there's Stoke-on-Trent; the council were selling houses for £1 on the condition that the new owner renovated them to code. Otherwise, rural living in Scotland is also quite cheap.