Oregonblitzkrieg, as I posted on another thread, you can get free STCW classes and an AB Special, if you attend the SIU apprenticeship program in Maryland. That would be the quickest and cheapest route, if you can get into the program and put up with the regimental-style stuff for a few months.
I’ve looked around, and most jobs on the internet require STCW/BST for entry level OSs, or so they say. Exceptions are NOAA, which provides training, and MSC, which also provides training, but it seems there are never any entry level OS jobs advertised for MSC, (I’ve been watching their site for several years). The Norwegian Cruise Line (NCL) cruise ship in Hawaii also provides BST to all their employees, in fact, they used to to send their new crew to train at SIU’s facility. NCL runs the only large cruise ship that requires American employees, but I don’t know how to get an OS or wiper job with NCL, like MSC, they never advertise openings for those. It’s still a mystery to me where their entry level deck people come from. (if anyone knows, please chime in) As far as I can tell SIU places people with NOAA, MSC, and NCL, so maybe all the entry deck jobs are filled by SIU.