japan
Mine is worth $675. It has original hard case. It was shot only 67 times, and is like new. 6202443112
$375 to $700 depending on condition.
100-500 or so
100-500 USD
500 USD or so
500 to 750USD for a private sale depending upon condition. If yours is 'near mint' expect the higher portion of that range. Expect another 10-15% above that from a storefront. Ithaca imported SKB O/Us between 1967-1979 (approx.) so if your local firearm regulating district demands steel shot (vs. lead) for waterfowl and other birds, you'll want to ensure that the barrels are capable of that.
100-500 usd
http://ithacagunrepair.com/page14/page13/ sells some SKB manuals. You'll have to look closely to see if they have the exact one you want. Good luck!
Send me your email and I'll send you a scan of the manual. I need the owners manual for the Ithaca SKB 500 O/U shotgun. Please e mail me with a PDF file or scan at temcowilly@aol.com. Thanks Bill
Blue Book of Gun Values will help.
Ithaca 500 model shotguns were imported by SKB (japanese manuf.). They are currently selling on gunbroker.com for $600-$1200 depending on condition.