John Williamson wrote:

It seems that that about a grand a square metre is the norm,

Certainly that's a number I've heard bandied around before.

so thirty should cover
the build for a small bungalow replacement

Wouldn't e.g. 6mx5m be a tad on the small side? The 'Acacia' is the
smallest two bed bungalow on that ScotBuild site and it's 65m^2

http://www.scotframe.co.uk/web/site/SelfBuild/HomesPortfolio/Bungalows/Acacia.asp

Certainly cheap enough to look seriously at the possibilities.

Have fun thinking about it ...