Ok fair enough, if you want 1600mm travel then the discussion is valid :)

Option 3 is to find out how much RM2010 ballscrews cost:
Aliexpress.com : Buy Anti Backlash Ballscrews RM 2010 L1000mm*2pcs with 2pcs SFU2010 ballnut for CNC Machine from Reliable Ball screw suppliers on BST AUTOMATION

If you wait for the seller to be online or just send them a message I'm sure they'll give you a price for RM2010-1800mm (or whatever). They also have RM1616 and RM2020, which would also be good since then the critical speed is no longer an issue (you can gain back the resolution via the pulleys):

http://www.aliexpress.com/store/3147...Text=high+lead