the older ones, especially have dropped a fair bit in the last few years. The spyder threaded ones usually go for more. Your's is very nice with the addition of the pump changer and t stock. nice collection of barrrels. Take that 21" one to the field and everyone will start making comments about pumps being snipers lol. The barrels could go anywhere from $25-50($30ish is probably realistic) depending on brand, condition. Unless they have wedgits most of them would need to be freakbored for today's small paint.
I would start the whole kit at $300 and go down from there. Probably get more money selling the gun with the stock barrel and one other barrel and then parting the rest of the barrels. gun and two barrels maybe start around $200? Not really sure these days. Most people don't know how awesome they are.
I personally might be interested in buying a barrel off of you. I like that sp AA that's on the gun in the pic.