I used to work in a dental lab, and the charge to make a nightguard was 80 to the dentist. The dentist can upcharge to anything he likes......good money maker....He makes the impression, and sends to lab....Dentist might have to make adjustments when its placed and periodically over time. Very expensive item that costs nothing to make.....
they are expensive due to office overhead.... staff, lab fees, materials, follow up adjustments etc etc etc etc etc. you get what you pay for.
I do not know the reason for the fees--that is something that you will have to discuss with your dentist.I would be interested in knowing what the difference between the $800 and $300 mouthguard. Itis possible that the more expensive one is made by the lab and the less expensive one is made by the dentist .Get a feeling how long each will last and then make a decision.