Singer sewing machines have been around since the mid-1800s, with similar machines also made by Howe, Wheeler and Wilson, and Grover and Baker. Value resides in the condition, working parts, and condition of the wood. If you look online or on Craigslist, you will see a vast array of values.
In order to learn more about your machine, check out Singer's online site. If you find the serial number on your machine, you can learn how many of that model were made, and the manufacturing date. If you see a date on the machine, that may indicate the patent date, not the date that specific machine was made.
Once you identify your machine, you can find parts, accessories, and a manual online. I had an old treadle machine and my son found the manual and repaired the machine so that I could actually use it. Many of those old machines were torn apart to use the cast iron bases as bases for tables, often marble topped. (I have one of those too.)
For more information on old sewing machines, you can check out the International Sewing Machine Collector's Society.