Steelsewing

Treadle machines are still fairly common to find. The market value is all over the place. Where I live, I can buy an old Singer treadle for anywhere between 50 bucks, or 500. leonf is correct in that many of the older machines used shuttle bobbins instead of what we're used to. The 'simpler' easy to find treadle Singer 66 model has a round class 66 bobbin - a little more common, and you can occasionally find Singer model 15's in a treadle. (class 15 bobbins). Each of those take a 'regular' needle and bobbins you can still buy in a store - and the bits and parts for the treadle assembly are not terribly difficult to find. The White Rotary machines (FR) are also somewhat common, they have they're own bobbin, but it's still normal-ish to what we expect today in a sewing machine. The value of treadle machines is often in the eye of the seller... you can still find used treadles originally made in the 1950s for a reasonable price, but machines made in the 1850s...maybe not so much. Pre-1900 treadles are in a different market as collectables/antiques and may be difficult in finding parts.