the PADI dive course is the PDAI dive course no matter where you go
Actually that's not so. It varies enormously, and many instructors teach well below PADI's standards. Read Scubaboard for a while and see how much the "standard" PADI OW course in fact varies. The "approved course" is a minimum that some instructors go beyond, because they feel it is otherwise inadequate. There have recently been several controversial and to some extent acrimonious threads on precisely this subject. I am also a PADI IDC Staff Instructor and have been doing this for a while, so I've an idea of what I'm talking about.
On the actual price, make sure what it includes. The elements that go to make up your bill are the course cost itself, any park fees incurred, the cost of a manual, sales tax, and the cost of certification. Plus perhaps a surcharge for using a credit card. Honest operators either bundle it all together and thus look relatively expensive, or itemise the costs and point out that you will have to pay them all. Less scrupulous operators (and I can think of some here in San Pedro) leave out items and don't tell you about them until they hand you the bill.
So let your friends go to whoever advertises the lowest price and I hope they have a safe, instructive and enjoyable time, whatever it ends up costing them.