Thanks for the response so far.

Over the last few years i've done loads of research into mdf based machines...it was only 18 months ago that I finally had space to build one after collecting electronics etc over a period of years.
So i've had a learning curve already - ultimately I can see that mdf is going to limit me (as well as annoy).

Right now, after having a quick look into material costs a bit more closely, I don't think I can go for a new full ally profile build as I simply don't have the funds. From a quick glance - ally box & steel box don't actually seem to work out that much cheaper.

My current thinking now is to start upgrading my existing machine into more of a hybrid - then keep upgrading as & when I can.

The biggest problem I have at the moment is the main table/base - it just isn't up to the job. So i'm thinking about making some sort of metal frame for the table - then attaching the rest of my current setup to that.

Tool wise I have most hand held power tools (inc angle grinder & jigsaw) with a circular saw mounted as a table saw & also a router table....no pillar drill. I plan on getting a better table saw & also a chop saw at some stage soonish as well.
I have very little experience working with steel...i've done much more with aluminium & would be more confident working with it as a result.

As welding isn't an option - how would you suggest creating an accurate solid frame out of box stock?
I have a metal supplier near me that could in theory cut pieces to length for me - but how best to join them?