Ray,
If the weapon is in the condition claimed, then $300 is a bargain. Walther has, and continues, to make a quality product. Unlike some other big names (for example: Weatherby) Walther has always manufactured thier own with attention to detail, materials and craftmanship.
I say go for it. You may find it worth more than you're currently paying.
Check out
Fjestad's Blue Book of Gun Values.