Help deciding on XBMC HTPC

Hello all, I have spent the last couple of hours reading many articles and boards about different ways to get your hands on a reasonably priced xbmc system. So far the most suggested option is the acer revo due to its Nvidia ion GPU which can vdpau. I understand why it is considered the best price-wise for a nettop but was wondering if it would be cheaper to build my own mini ITX machine.

I beg for your help in finding/building a cheap XBMC machine.

All parts must be available here in New Zealand   . This is the major reason for the horrendous pricing and why I need to find it cheaper elsewhere. (Ebay is fine)

I need to play 8GB+ HD movies in 1080p either via USB or streaming through the network, I have a USB blu-ray drive and would be able to use that instead of buying an optical drive. The size of the machine doesn't matter much but I would like to get it as small and quiet as possible. I don't care how it looks I just don't have the money to buy an expensive system and XBMC is supposed to be pretty damn good anyway.

Is the cheapest option really to stick with the acer or can you guys find a better alternative?

Thanks!!