This past December, Best Buy had clearanced out a 50" LG Smart 3D Plasma TV for $399.00. It was 720p and came with no glasses, but the tv was awesome. Great picture and awesome color. Nowhere near my Samsung 55ES8000, but still an awesome TV for $400.00.So yes, you can get great 3D tv's for less than $500.00 nowadays.
720p on a 50" tv. Meh.
I mean, if you have bad eyesight and can't tell the difference between 720p and 1080p on a 40+" HDTV, then sure.