Don't listen to the naysayers. You are on the right path about doing your own frame.

There are only 2 things special about Samsung's Frame TV. 1) How crazy thin to the wall it is. 2) the art mode.

The TV itself is nothing special and the bezel around it is plain Jane. They charge $100 for a piece of vinyl that changes the color.

The last 65" Frame I did, the customer was not impressed with how it looked on the wall. The Mrs. was expecting more. She ended up looking over this website below and ordering a real frame to put on the TV. She installed it herself and it came out great. She like how it looks now.
[Link: framemytv.com]

So.... How much money could one save with using a regular TV, thin mount, and a custom frame? It depends.
The Samsung Frame is one of Samsung's higher end TVs, so to equal the picture quality you have to use a higher end model from other manufactures. The overall savings would be $0.
But if a customer was just wanting the art look and didn't care about the actual TV picture quality, then it would be possible to save a few hundred $$$.

The problem with all this however is Samsung's "art mode". If the customer actually wants art to display on the screen when not in use, no other TV (that I'm aware of yet) has a mode that will dim down the screen and work like this.
You can easily create a screen saver to display on a customer's TV with artwork. But the dimming of the screen and changing of the video settings is not something I have seen, that you can recreate with another TV.