We picked up a Singer 241-12 (similar to what Makitmama posted) in it's original industrial table for $100 locally (I have good shopping "fu") They usually run from $300-$600 in good shape, with the occasional deal under $300.
I bought this 1948 machine because it was a good deal that I planned to flip, but once my lady tried it, all bets were off. This machine runs up to 3000-5000 stitches per minute. We are still only running it at about 1/2 - 3/4 speed because we are not used to it yet. But it sure make short work of long seams.