Fabricate and machine steel router frame

I'm looking for someone to fabricate and machine a fixed gantry CNC router frame.
The design hasn't been finalized at the moment because I would like some input from the manufacturer about what can and cant be done.
X axis length will be 650mm, Y 850mm, total gantry height 150mm ish.
Motion componants will be hgr20 with ball screws.

Im located close to Manchester, would be willing to travel a little to pick up the finished frame.

Current plan uses 100x100x5mm steel box section. Ideally the gantry would be bolted on to allow easy transport.