I don't mean to disrespect you as an artist or person or belittle your effort and work. It is still very expensive for $4 a picture. The comment 'oh its cheaper if you follow me on patreon' still sounds really bad. Yes that isn't exactly what you said but that is how it sounds to me when I read it especially with "and wait for them to be sent" which in itself sound extremely yikes.
All of this really makes me run for the hills not buy the art outright nor provide money in a monthly subscription.