Ok - it looks like i'm looking in the £200 ballpark which is a lot more than the DIY route...but I know i'm not looking at like for like here.

I'll carry on drawing up the rough design & then look at the exact rail lengths involved.

If i'm using aluminium profile for the table sides (I think the sides are 80x40 from memory), whats the best way to attach the supported rail to them given that the mounting holes won't match the slot spacing?