Take a USB install of OSX, a USB keyboard and mouse, then look for cheap "broken" macbooks on ebay/kijiji/whater local website is popular. Make an appointment to try the macbook with your stuff. Test whether it boots. It it does, negotiate a low price - don't bother more.
The basic idea is some macbook have dead screens, HD problems, keyboard problems- and they can be purchased on the cheap.
If you are bootstrapping, it can be interesting. Got a top of the line macbook pro for $200 that way- it had been soaked in beer causing the HD and keyboard to fail.
With an external keyboard and a USB key until I managed to replace the HD, it worked just fine as a dev station.
I initially had this idea after experiencing the same problem with my previous macbook due to a leaky roof :-)
