You can't buy an SKS for $200, a Winchester parts gun goes for $300-$400. So bottom dollar $500, it might sit on EE for a few days but it will go for that pretty easy. it goes up from there depending on condition and (factory) features (like custom sights, checkering, butt style etc.)
I believe the documentation from the Cody museum costs about $75USD - so it's not always worth it if the gun is in an 'off the shelf' configuration - that only helps when the gun was a special order, i.e. fancy stock, checkering, short magazine, custom sights etc-etc-etc.
You can generally tell how 'messed with' a gun is by looking at the screws (on the front barrel band, middle band, sides of receiver and tang) if they are marred you at least know that 'not a gunsmith' has had it apart, at that point you are in a who knows what was replaced situation.
if it has no custom/special features then you probably have (as tokguy stated) a $400-$600 (depending on condition) gun and not worth getting the Cody letter.
Also - "looks working" those 94s can have a lot of issues that look fine but make them completely unusable... for example, when the link gets worn cartridges will start feeding out of the magazine under the carrier when it is in battery ... you get to take the gun apart then. hammers and sears wear making it not #### ... etc.
you really need to shoot it to see if it actually functions as advertised.