Here are a couple of good inexpensive options. Hardboard cut to size and either held in place with some hardwood trim around the edges of the door or just held on with good old carpet tape. Another good option that can be held on in using either of the methods above is to use some close out Pergo style laminate flooring. The finish on the flooring lets glue and oil wipe off very easily and will take one hell of a beating. Plus if you you buy a closeout box you will have a couple of extra pieces that you can use to replace any pieces that get damaged badly.
I put polyurethane on mine. Though I saw a guy that had a piece of bowling lane that used some heavy duty clear epoxy type stuff you can get from HD. It looked super slick.
Half of mine is covered with a 1/2 inch steel plate. The rest is whatever oil, paint, diesel fuel, dust, and other things that have encrusted it over the last twenty years.
That's what I use on my woodworking bench. I wipe it down every 6 mo to 1 yr with BLO mixed at 2/3 turpentine and 1/3 BLO. It makes the top a little slippy so projects move about with ease. It is easy to clean and while glue does stick to it, the dots just pop right off when hit lightly with a chisel.
Be sure you get a bench brush so you can dust it frequently and keep it "project ready".