Could the DH be a typo? If it was DB it would be more accurate as the Ulster engineer David Brown, a former tractor maker, worked with Aston to produce many great cars and the DB moniker was given to many of thei subsequent models.
I think the DH just stands for drop-head. The original V8 Vantage came in convertible form (but not the later Virage-based one) and that price would be right for one of the later ones.