Sterling silver sugar casters were introduced to Europe in the 17th century. By the late 1600s, other casters were used for mustard and pepper. Usually, the older casters are in the lighthouse style, a simple cylinder with piercings on the top. Being rare, these would be the most valuable and can sell for thousands of dollars. Later versions include Queen Anne, a stouter style with elaborate piercings and acorn, ball, or pineapple shaped finial. Vase-shaped obviously resembled a vase. Baluster style was wide at the bottom third, then slimming above.
When casters were mass produced, the silver that made up the body became thinner so needed a wider or weighted bottom for balance.
Look around online at sugar casters for sale at antique sites. You can check out a book such as "The Book of Old Silver: English, American, and Foreign" by Seymour B Wyler, or "Pocket Editions Jackson's Hallmarks" by Ian Pickford.
Check the bottom of your caster to see if there are any identifying marks.
You can also call your insurance broker who can recommend an appraiser.