Bob- It totally depends on condition, maker, and what a buyer is willing to pay. Saw a mint blade marked, not dated Robeson(RCC) w/M6 leather scabbard sell for $2761.00 a couple of weeks ago. That is the highest I have ever seen one go for. Generally blade-dated or blade marked are considered rarer versions of M3's and were the first versions issued out in WW2. Most have seen some mileage. There is really no set rule. Depends on the maker, how many they produced, how many variations, condition and scabbard. For some great info on M3's you might want to invest in Coniglio & Laden's book "The US M3 Trench Knife of WW2" good reading. They are now working on an update to include info on the M4 Bayonet. Also as mentioned before follow ebay sales. You can really get a good handle on values, that's what I do. I've made some good buys at shows because I had a pretty good idea of values. It pays off.Good Luck! SKIP