As someone nearing the end of my first build - that's a good idea.

What's the aim though? An MDF machine more solidly constructed, or something more fancy (alu sections, etc)? For £200 it's probably either sticking to MDF, or possibly alu with leadscrews rather than ballscrews? But alu would need decent rails to get any benefit - is that achievable with £200?
What are you thinking?

Anyway, I'm happy to contribute my learnings so far...
1) Leadscrew whip is bad.
2) My next router will be more rigid (although the secret aluminium skinning stage for this router isn't complete yet).
3) Ballscrews would be great, but would also be ruined (and pointless) on an MDF machine.
4) Cutting alu takes a properly sorted machine.