It's unfortunate you feel this way. I think $600 to attempt and achieve something of this degree of difficulty is reasonable, when most dentists (myself included) might well have advised whole new crown at a higher cost.
I should have had the endodonist temp glue the crown on, then made an appointment for the next day or two to come in where I could then ask about the cost. She fit me in spur of the moment. However, it was she who told me to have the endodonist give her 30 minutes head start and I could come right over, which I did. I wasn't in any particular rush to have the crown cemented on. I was almost made to feel that it was no big deal to have the crown cemented back on, which is why weeks before she just needed 30 minute prior notice. I agree with you that the chances of the crown fitting back on perfectly isn't a given. Nor is it a given that it was merely the cement that gave up in the first place. It could have gotten mobility because of decay, like you said.
Anyways, maybe I'll stay with her as my dentist, now that you replied. I have to say, it was a real shock cost wise. Also, there's no telling how long her minor tooth build up job will last. She didn't prep me about how the crown might not fit back on perfectly. She made it seem like it was no big deal. $600 is a big deal.
Edit: When getting my teeth cleaned the hygentist alerted the Dr. of "mobility" of the crown. She (the dentist) was able to pop it off rather easily. After reading your reply, I suddenly see that mobility of a crown is not a good thing. No, it's not just the cement giving up. I knew that afterwards by reasonable thinking. Then again, what's best for the patient, the patient doesn't always want to hear, cost wise. One last thing in hindsight, I still should have let the endodontist temp cement the crown on. That way I wouldn't be crashing her busy day, which she just happen to be having, lol. She made it seem I had a good chance of re-using the crown tho, when having my teeth cleaned. I wish she wasn't so rushed that day. I bet you I could have asked for a lesser price. She took a few ex-rays before the final cement. Very thorough.