I bought a National Two Spool treadle machine last week at a garage sale. Can anyone tell me how to find out what it is worth? It has the can inserted which I can see but I have not removed it, nor do I know if it operates properly. The machine has many attachments and the original manual plus a newer manual. The cabinet is worn and used but intact and in reasonable condition for a machine of its age. I posted about the machine on my blog and a reader would like to buy it from me. I may want to sell it but I don't know its worth. I checked on ebay and saw Singer treadles listed for auction in the $300-$500 range, couldn't believe it. I assume the two spool is rarer and possibly worth more? I'd appreciate any comments about this machine. Thanks.