yes, because the average joe can replace a water pump. /facepalm
$500 for 4 hours of work is about average at a garage. No ones ripping anyone off, you needed a water pump, you were able to install it yourself. grats. You saved yourself labor fees.
You saved yourself vehicle downtime, the inconvenience of finding alternate transportation including a ride from and to the dealership unless they provide a loaner. There's also the inconvenience of unloading anything valuable from your vehicle and reloading later.
You might have to pay to tow it there and wait even longer if their schedule isn't open to get yours done right away, and they may not have the part in stock. Many shops overbook for a smooth interruption free workload, so there are many reasons it could take a while.
You may have saved yourself time. Many people would experience more interruption in their life to take it somewhere, drop it off, wait, and go get it, than just DIY. Most water pumps don't take 4 hours, not even if that's the billable shop rate, and that's DIY while a shop mechanic experienced at that model, will be able to do it in even less time. Is it a ripoff to be billed for more hours that it took? "Maybe".
You can choose to Do It Right. The typical mechanic at a dealership is primarily interested in conversion rate, getting it done quickest way possible. They may screw something else up in the process, then you have the fun of trying to prove that and either way, hopefully you notice before leaving the shop or you're headed into round two of the repair process.
You can buy a part with a lifetime warranty, which the dealerships seldom offer, and which usually only costs half as much.
If paying multiple times as much for a worse situation is appealing, have at it.