I've used a door with 2x4's for a table before, works well and is cheap provided you don't mind a bit of sway. I used it for a drymount press and rotary trimmer.
I found an old office desk that weighed atleast 350lbs waiting to be thrown out.
It was left outside behind an old building. Worked out very well, extremely stable..
Many drawers, etc. I used cinderblocks to prop it up, too.
Places like www.sciplus.com usually have surplus materials like 1 to 3mil vinyl sheeting with adhesive, great for covering your tables. I love that site.