At $200, "Cheap"

is a matter of opinion...
I hate to tell you but most common problems and complaints associated with long-term wear of almost every kind of external prosthetic "anything" (from breasts to limbs to ostomy products) are skin irritation, heat and lack of adhesion. There are solutions and work-arounds but some may not be be as aesthetically pleasing as others.
One could toss out her pretty bras in favor of those which offer more support and needing less glue. Pocketed mastectomy bras where nothing touches skin but cloth are OK but the problem there is the breast form does not really move with you.
I have no personal experience with Amoena prosthetics but we have a friend (cisgendered double mastectomee) who has worn a pair of their earlier "self adhering" styles for several years and swears by them - but she has also admits that she has to sometimes resort to her old mastectomy bras for a day or two every so often because of irritation.
As for the vendor to whom you referred, many of their models are quite similar to the forms made by the same company who makes one brand of medical prosthetics. Also, from a quick view of the vendor's site, their prices seem to be lower than you would find at a medical prosthetic fitting house.
Susan