I don't find that outrageous, but it is on the high end of normal. I think you need to ask what else it includes, books, rental gear, OW fees, gas fills, instructor fees, DM tips, camping at the OW checkout, pool fees, etc. Someone else's $275 that includes books and c-card may not include the rest of the stuff I mentioned, and all of that is going to get charged to you one way or another. It's a fallacy that there are cheap scuba courses out there. They may range $25 or $50, but that's about it. Make yourself a matrix that includes those other things I mentioned, then ask where OW class is. I know a dive shop in Houston that will push you to do your OW checkout dives in Cozumel, adding an easy $1500 to the bill. Of course, you're in Cozumel....
If you do find a cheap scuba course, they are likely taking it out of the Divemaster and Instructor's hide (fees). Do you want to learn from the cheapest contractor?
It tends to be SSI shops that insist you buy your gear from them. It's part of their marketing technique. It isn't wrong, it is what it is. I'd like you to use pawn shop gear when I teach, because you're going to replace the fins a couple of times and the mask at least 3 times. Actually, I think it's a shame that dive shops won't let you try their masks, it lets you use 3 or 4 of them without committing to one, and when you find the right one, buy it then.
Our $275 includes everything and we are an SSI shop that doesn't require purchase of equipment from us.