McKeown's has the Envoy 35 at a whopping $40 to $60, give or take. Is this the one with the 7-element kominar lens and a copal shutter?
whichever, the whole range is of the low-cost variety, so having it serviced will definitely not pay you or improve the value of the camera much.
On the other hand, if it is a camera with a good lens, and you want to shoot it, cost to have the shutter serviced will probably be $75 or so, plus shipping, and then you will have a reliable rangefinder shooter.
Another thing you might do is sit in front of a bad movie on tv and wind and click the shutter a few hundred times, see if the shutter blades break apart after having sat stuck together a couple of decades. If that happens, put film in it and fire away.