What is the value of a 1929 singer sewing machine today?

Try looking on ebay at completed listings to see how much they sell for. It depends on the model, a common machine will be worth less than a rarer machine. But generally, anything from about £60-£250 or sometimes even more for a working antique singer treadle is realistic. Btw, ebay isn't the best place to sell such things, as they cannot be posted, and the chances of someone living near enough to collect it AND who is willing to pay for a big van or something to transport it AND who particularly likes your machine is slim.