Went to the Norwegian website where it advertises one-way BWI-GDP for $49, service on Tuesdays and Saturdays. I couldn't resist... An early December Saturday is available for $69 but the flight arrives 18:15. The return the next Saturday is priced at $149 but departs GDP at 08:25. Add $25 each way for a bag and reserved seat. To compare, the UA non-stop from IAD on the same Saturdays is currently $520 R/T.