What does it say on the tins, if anything? If it is US ammo, you can find out the cost per round that it is selling for these days, at gun-deals.com where commercial ammo is selling from 29 cents a round for Wolf up to 55 cents max for ball ammo. But that is commercial stuff. I would not downgrade USGI stuff to the bottom of that range unless you are needing to sell it off fast. Then I guess if you were to undersell say, Wolf at maybe 25 cents a round, you could make a good piece of money off of it, probably more than you payed? If it is corrosive Chinese LC 52 copy stuff, get what you can for it before they find out what they are buying!
Your gun is like your nose, it is just wrong for someone else to pick it for you!