Yes $250 would be a good deal you can always sell off what you do not need.
Bottles being so heavy I would work a deal with a local welding supply for a few smaller bottles one K is worth a few 20# JMO in value.
I wouldn't do anything rash, hang onto a few corny's you may expand needing them in the future.
On the larger bottles do not let someone snag them on the cheap (you getting screwed while they smile) ok?
Check for purchasing or replacement of those C02 bottles to get cost replacement value, add a hydro fee as well filling to know where your at in value you have. The "K" bottle is 9 1/4" x 60" tall x 135# tare wt plus app $45+ to have filled.
Only when you decide on selling, i'd keep one large bottle and a few corny's plus regulators as spares.
Are these Pepsi corny's? What would be your selling price if available as I am looking for two of them in ball lock top fittings? Let me know after you gathered more information on your collection. Thanks. Carl in Calif.