A ballscrew kit can run under 1000.00 and the mounts can be made or bought for ~500.00, I converted a series 1 2J and then built a z axis conversion for it. I could not have been happier with the results.
for about 3K, I bought ball screws, mounts, motors, power supply, gecko G203V's and a smooth stepper. This was all money WELL spent. Add this two a 250.00 BP and I now have a 10K machine for 3250.00
I can get you an itemized list of what I used if you are interested.
I got my screws and mounts from Mel. I can get you his info if you need.
Convert with ballscrews (ground) and you wont be sorry.