Try office equipment salvage or more specifically graphic arts or print shop salvage businesses. Four of us bought five light tables a year or more ago, east of Cleveland, OH. The tables were similar in size, but some features were different. Mine is 30x44" and cost $20 or $25. The business was going to scrap them so this was good money for them. Mine was made in Germany, raises, lowers, tilts and has four light tubes. I would guess by the quality it cost a couple of thousand $ new. If you can find a place like this near you, have a SUV-van-pickup to haul it, have the space to house it, you can't afford to build a small one yourself. It is great to be able to lay out and compare a whole series of 8x10 or 7x17 negatives before you decide how to print them.
John Powers