It isn't that hard to dig up the production numbers on second and third generations and to be able to tell them apart. You can even check on the numbers of each caliber and the finishes.
IMO I have a hunch it's a third generation, prices I have seen could be anywhere from $800 to $1,500 depending on condition and if it had a letter from Colt authenticating the caliber and finish. cowboy action shooters are probably the best folks to ask as they have the biggest market for SAAs these days.
If it were a true second generation nickled .357 it would depend on production numbers and condition but I suspect it would start a little above where the third generation tops out, say $1,500 in a low but complete condition and go into the stratosphere.
That is a rough guess. I have a friend who owns a gunshop and he turned up a very, very nice example of a particular SAA. He offered it to me for the top end estimate he got on it, but I decided to buy a truck instead.
Buying a Colt SAA is a tricky thing these days. The difference between generations means a lot to hard core collectors and it is easy to make a mistake, a very costly one.
For instance, you say the grips are "Factory but look cheap". That is a flag to me. Colt factory grips never looked "cheap" on a second gen, and if they are the gutta percha originals and you think they look "cheap" I (and I say this for your sake) worry that you may not have an idea of what you are really looking at.
More people get burned buying SAAs than find "undiscovered gems" these days.
Investing in something like that takes a lot of knowledge and experience to do well