next time can you not post in caps please :D

your budget should easily get you the machine you require.

what kind of tools do you have to build the machine? do you have a mig welder? tap tools, pillar drill chop saw? all these things are the first things that spring to mind.

i'm building a machine a little smaller than yours 400 x 480mm and my cost is easily coming under £1k and thats with a 2.2kw water cooled spindle, 16mm ballscrews and rails all built in steel and all the electrics included. obviously there are some places i have cut costs, so with your budget you could easily build the machine you require and as strong and reliable as you require.

best thing to do is work out a list of tools you have to build this, your skills in metal working and possibly have a look at some of the work logs on here and start to come up with a rough design in google sketchup, there is a really good thread on here with hints and tips on using sketchup including some videos.

just be prepared to go through a couple of redesigns and come back here for advice between each one to make sure your on the right track