If you get just the rifle, depending on it's condition, maker, markings, if it's a G43 or a K43, you'll pay anywhere from $2000 to $3500, maybe more if it's one with rare Waffenampts on it or something.
Real scope mounts are worth a small mint all by themselves. ZF-4 scopes are almost plentiful and they can be had for relativly inexpensive ($500-$600)...but an actual German WWII G43 scope mount is almost worth as much as a beater version of the rifle.
I lucked out and picked up a very good condition 1944 a block ac (Walther) G43 with real scope mount, and artic ZF-4 scope (the type that would have been used on the Eastern front) for $4k out the door. I didn't overpay, and it's probably worth more now.
I wouldn't recommend a G43/K43 as your first collectors-type rifle...start small and simple, things like Garands, 98k's, Arisakas, etc...finding a real matching K98k these days is more an exersize in patience than it used to be! (Not to mention much more expensive than it used to be..)