Have you thought about getting an old Atari ST? These a dirt cheap and you can generally find one with a copy of Cubase or Notator included in the price. I used my Atari 1040STE with 1MB or RAM and Notator 3.1 with little problems and it only crashed a few times in a couple of years (NB- all computers crash at some stage!!!!). If you can get an Atari with 2 or even 4MB of RAM all the better. I now have an Atari Mega STE with 4MB RAM and a 40(!)MB hard drive. I run Notator and Cubase from it with no problems (except that it doesn't work well with my Korg Z1 or Triton Moss board- it seems to randomly change parameter values at the start of a song and then goes back to normal after a few seconds!!!!) Otherwise, NO PROBLEM.

All Ataris have a built in Midi interface which saves you more money buying a separate one on a PC or Mac.

Fact remains that many home (and even pro) studios are still using Ataris because they are reliable and get the job done- AND THEY ARE CHEAP!.