I think Mesa / Linuxcnc is a step too far at the moment, I looked at Mesa/Pathpilot and discounted it for the same reason. I'd have bought the CSMIO IP/M in a heartbeat if it supported independent axis homing for slaves and I still haven't ruled it out completely but manually squaring the gantry seems like a bit of a fudge.

The Purelogic board looks interesting but I can't find any English documentation, and I'm guessing support would be an issue too.

The warp 9 ESS looks well supported but the cost with a PMDX-126 and shipping/import duty/vat puts this combo very close in price to the CSMIO IP/S so that puts me back where I started, either the CSMIO IP/M or a cheap standalone chinese all in one to get the machine moving and making chips.