A couple turns of a set screw and a small rubber O-ring pretty much make the safety go away. This seems to be what the cowboys that shoot these do. In competition or participation in the sport of CAS, it gets real annoying when the safety is on. I O-ringed my 1894 and never had an issue. Personally I don't put any more value on a JM than I would for a new REP one.
As already stated there are different models, the round barreled "1894C" is the cheapest. It also only has a 9 capacity magazine that makes it a harder sell to the 10 shot cowboy crowd. A typical stage calls for 10 rounds in the rifle, empty chamber. The "1894CB" is the more expensive model.
Because Cowboys demand a bit better function from their rifles than hunters/plinkers, the feeding mechanisms have been improved in recent years, post JM. Specifically, the lifter has been redesigned to allow for the rifle to be run faster without the "Marlin Jam" occurring, until the rifle has significant wear.
Value: Same as a new one for insurance purposes, only because finding a reasonably priced used one in good to very good condition isn't always easy.
In good to very good condition, and with a low round count, if I found one for $450 I'd buy it, update the lifter and have it slicked up by a smith and be a happy camper. In the back of my mind I'd be thinking that later on I shouldn't have any problem getting $650, especially with the mods. Half the time the gun stores are out of stock, so that keeps the price of a used one up there.
I occasionally rent a table at our local gunshows and I've found that to sell quickly, you need to leave something in it for the buyer. Also, if a dealer comes up and buys it before the show starts, you had it priced a bit too low. Same as here on CGN, if it sells within the hour, you could have asked more. I had a typo once on my listing, gone in 10 minutes, now I double check before posting. If you have bumped it for the third time, too spendy.
With no picture, it's hard to give a definitive value. Even some of the JM's had some terrible fit issues. A rusted or pitted bore is a real value buster as well. Marks on the hammer from a spur being used when a scope was mounted, that knocks off a few bucks as well. Plugs missing in scope mounting holes, a detractor as well.