This is almost like asking a gun value question without offering any information other than caliber.
Not all hulls are alike. What make are the hulls, are they once fired, what condition are they in (did you fire them or pick them up after lying on the ground all winter). These all matter.
Reloaders will pay for once-fired, premium factory hulls in top condition. 12 and 20 gauge Winchester AA, Winchester AA HS, Remington STS and Federal Gold Medal (paper or plastic) generally go for around 5 cents apiece.
You can usually ask 10 cents apiece for 28 gauge providing them are premium hulls in the same brands noted above and once fired. However I wouldn't pay you anything for Federal Gold Medal 28 gauge. I've had very bad experiences with them.