My new table saw is very heavy and difficult to move. I made a mobile base with retractable casters out of wood and hardware that I had in my shop. The only thing that I purchased was 3" casters from Harbor Freight. This mechanism is very easy to operate and makes moving the saw effortless.

I had built something similar on my old saw using the same lever action setup, but instead of building a frame around the legs, I attached the supports to the inside of the legs and the casters hinged on those. I also used smaller casters (2"). It's definitely better than nothing, but with the casters so close together, it makes the saw a bit unsteady. The wider footprint of the new setup and the larger casters make for a much smoother ride.