No shop can make any money doing oil changes for $25-30 bucks, especially dealers, who have higher overhead. They charge that low price to get you in the door in hopes they find another problem that they can charge you for (I'm talking about a legitimate problem here).
So, if you can get it cheap, of course go for it. But to say $50 is getting "ripped off", I disagree because that implies the seller is making a huge, undue profit. Because many shops use the oil change as a loss leader, the higher price is probably not "competitive", but I wouldn't call it a rip-off.