I'm pretty sure I did not buy directly from TriMark - but I have not found my receipt yet. It seems to me that the manufacturers usually charge more than third-party retailers. A third-party retailer may sell cheaper because this is "old stock". You could try Googling "TriMark 030-0450".
In the case of this door handle, the link I provided says that handle has been replaced with a newer model (030-1450) (more rounded edges). If that newer model fits the opening nicely (covers the unpainted edges around the opening), then you may want to consider going with the newer model. I think it is better looking and it may have some internal improvements.