i have a couple rugers. the red eagle you mention and a Mk 2 govmt. ive shot the red eagle, but not the mk 2, so im not sure whats different. i havent even opend the box to the mk2 since got it. im thinking the mk1 didnt have the slide release, only the safety.
iac as to the value.
if you can, find a copy of the Blue Book. the 30th ed is out now, but usually the values dont vary alot between consecutive issues.
for your red labe, the value will vary with condition. since you dont give the bbl length, i will assume the "standard version"
95% - 500
90% - 400
80% - 265
you may want to check the gun auction/selling sties and also check the "sold" items too. then i would print some out and if you can find some with similar conditions or ones that bracket the condtion you have. i would also show them to the seller so if you decide to make a lower offer, it will show youre not trying to screw him.
btw, if youre going to buy used guns you should get a copy of the blue book. even a used one. it give you alot of info and vaules.