You won't find them cheaper for sure and only BMW makes them.
Thanks for that. Having restored cars for the past 20 years, it's unlikely BMW "makes" them but I'm sure they order them from a company which has the mould and manufactures the rubbers or seals for BMW.
If anyone is looking, Tomkinson most recent prices for the door seals are;
Part # 51-71-6-754-282 $241.38
Part # 51-71-6-754-283 $235.60
Your first photo shows the BMW part number for the firewall pad. The seal at the trailing edge of the door is 51216740180 and 81, L and R if that's what you are looking for.
Under the door is, 51216740185, photo 2 is the seal in front of windshield 51715780175. Photo 3 does not belong anywhere.