$600/axis sounds pricey, automation tech sells a 3 axis kit for $320/axis plus the belts and pulleys for gear reduction. If you're willing to wade through broken English manuals and take some risk you can get an AC servo set by ordering direct from China via AliExpress. Ballscrews are also a lot more affordable direct from China, that's how I bought mine. I'd want some large diameter (20-25mm) precision ground ballscrews with preloaded double nuts for the most rigidity.

Got some drawings or models of the final design or do we have to wait till the build is complete!?