I hate to cast a shadow of suspicion over the forum, but "1730" IS a brand name. If the bottle is black and the 1730 is serigraphed on the bottle in big reddish stylish print, then it's by no means a vintage date. The price should have been high but not ruinous depending on its real age ($30 to $100) and the producer could be either Pilar Aranda or Garvey, especially the latter. Garvey has bottlings of all types of Sherry in a 1730 lineup both in V.O.S. (20+) and V.O.R.S. (30+) levels of age. Notice the "+" which means anything over 50 years of age (which is in fact the case of Domecq's top bottles, for example) can only aspire to be identified as VORS though almost twice the age.
This is by no means intended to disappoint you: consider that if I'm right any of you could repeat the experience either by visiting Spain or by checking out the sherry retailers around your area...Besides, I bet the U.S. pricing of sherry will not be brutally unfair, as sherry producers are kind of desperate for promotion abroad.