Unpopular opinion: I don't see a problem. You want a non srd class and race combo, put some skin in the game and buy it piecemeal. The dm likely had physical copies of tons of stuff and has spent a lot himself. Dndbeyond is a way to have players use an official character builder and not have to figure everything else out and get a phb etc. The dm is already running the campaign for you guys. It's not unreasonable to ask that you pay your own way when you want to do something that's not already free content from wotc. The character builder enforces creation rules and formats everything so all players have the same sheet structure.

Commerce the downvotes.