the pocket hammerless colts are excellent guns, made when guns were steel. they have great reputations, thanks to the john browning design.
as for the guns you described to start a collection, pass.... if you want to start a collection, buy guns with a high 90% rating and put them away.
if you wanna shoot them, then buy them and refinish them if you want pretty and then shoot some more.
they are gonna be fine with modern ammo if they have been well maintained.
what to offer?
well the dealer has to keep the lights on and pay the guy behind the counter, he isnt gonna drop the price much, unlike a car that gun will not depreciate sitting there.
start low, see if he haggles, when you reach your best price and he wont budge, shake his hand and leave... if he lets you get to the door, you really were too low.
and for god sake, stop drooling on the gun, he can see it and KNOWS how bad you want them.
last 1908 .380 i saw was 95-98% and was selling for just over $700. actually it was just sitting there under the glass.