$300 for virtually ANY Smith and Wesson is a great place to start unless it is totally ragged out. Even moreso if it is a pinned barrel, recessed cylinder, case hardened trigger and hammer, etc. Check the cylinder for lockup, and slop, make sure it times up properly, and you should be good to go.
ETA: Check the timing as follows. With a finger providing some resistance to rotation, cock the hammer fully to the rear. When the hammer locks back, make sure the cylinder bolt has fallen into place in the notch on the cylinder. It you still need to move the cylinder a little bit then you have a slightly worn "Hand" and it might need replacing. If, on the other hand, with a fully loaded cylinder and a firm and positive cocking motion it drops into the fully locked position then it might not need re-timing. Kind of depends on how picky you are about such things. If the gun is going to be shot A LOT, personally I would re-time it. But then I'm picky about such things. ymmv