I’ve found that the yagi element holders are quite expensive to print through a third party ( we use a local Fab Lab and they are very good so would recommend them). It is down to the mass of material and design.
More usually element holders a pipe clamps, like stauff blocks or cheaper versions like modified domestic pipe clamps but I have also used through beam holders. My old Sotabeams SB270 used drilled nylon threaded parts with the boom having a thread cut into it. Sounds flimsy but has worked for me on many windy Cumbrian fells for 5+ years. See photo.
Is it worth exploring either off the shelf or modified off the shelf items as well as printed parts?
