I must agree with Yukonho. Smaller is better, especially for a first build. That isn't to say though that a 4' by 8' can't be built for less than what most people pay for a used car (under $2,000). But remember that with a larger table, the motors must be stronger, as the mass of the machine is bigger. Heck...I'd build you a 4 by 8, mechanicals only for $2500, so I don't see why you couldn't do it!
Stop talking about it and do it already!!!!!
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)