If it is a home workshop hobby project, then dont even consider making anything close to a 4 X 8 table.
I started with a 12 X 36 inch table and I am making a smaller one now because I have designed a better table, and I have never come even close to using even half of my available travel. And the smaler machine will be more rigid and more accurate.
Treat it as a hobby project and you will be astonished what you can make when you get your table running, and you will actually stand a chance of getting it running.
You already have the 3 axis board and motors, so you can honestly build a great machine for 300 or less. If you want to splurge on THK slides and Ballscrews you will push the price up closer to 800 or a thousand.
My first two machines are MDF, and I use the first one (still building the second) for production work for 4 hours every day, and it cost me 400 Canadian dollars from start to finish including buying the electronics!
Do some reading here and you will see that everyone recommends a small machine for the first one. This is for a good reason, follow the advice and you will have an operating machine in no time, not a money pit sitting idle.