The linear bearings alone will cost that much.If I can find a good one, in the $150 to $200 range
It's really pretty simple.
Two aluminum plates, 20mm rails, and a 1605 or 1610 ballscrew.
20mm rails should give you enough clearance for the ballscrew.
Something like this, but with 2 bearings per rail.
Keep in mind that 3 Z axes will be very wide, and you'll need a long, extended gantry if you want all 3 spindles to be able to reach the table.