FYI...
The OOP SM-3 Seahawk is essentially the same booster as the PRO Terrier-Sandhawk. They are not cheap at auction but come significantly cheaper than the T-S. The advantage to the SM-3 is that it includes the transition piece.
In addition, the OOP Estes Python is also the same tube/fins as the T-S, and can be had much cheaper. It does not, however, include the transition.
Hope that helps...