Are these numbers still your rough estimate for cost? When the retroUSB AVS is selling for $185.00, those numbers are not likely to attract that many buyers.
I think the Walkman idea and button layout just does not work. The Walkman may evoke the pre-crash era to some extent, but it does not really make me think of video games or evoke the Atari 2600 in any notable way. Atari's cartridge design was designed when the portable consumer format of choice was the 8-track tape, not the compact cassette. I do like the woodgrain finish on the case, anything you can do to bring it out more would help evoke the Atari.
The button layout does not help. All Atari 2600 consoles had labels and placement where you knew exactly what each button did. The buttons on this device are too abstract. Which button is the game reset and which is the game select? (The one on the end that looks like |< is the reset, which is a good placement choice.) Why are the Difficulty Select and Color/B&W buttons so small and recessed?
Finally, the side loading cartridge slot gives some concern. Which way is this console supposed to be facing? One very dated element of the 2600 console design is the controller ports in the rear. But when the HDMI connector is in between the controller ports, this also suggests that it is supposed to face the rear. But this cuts down considerably on the controller lengths. But it does give better access to the cartridge slot. I suppose you could use it on its side, but the 2600 was top loading device and I believe that an angled or flat top loading slot is best.
What do the Play and Stop buttons really do? Do they turn the system on and off? Or do they function as a hardware reset? Does pushing Stop allow you to change cartridges?
Unfortunately the manufacturing cost for the plastic enclosure is really what determines the price. I've been toying with the idea of designing an FPGA based drop-in replacement for the Atari 2600 circuit board. Something like that could probably be sold for about $150 or so, and it retains the Atari 2600 styling since you are using the original 2600 enclosure.
I started this project not to sell a product and make money, but rather to create something that I wanted. I think that the Walkman motif works very well. It's compact, and it's something I can set on my coffee table, and play Atari 2600 games on my big screen TV from the comfort of my couch. Plus I think that the "PLAY" button is a cute pun. The connector placement is not an issue since the game console is right in front of me. The only long cable I need is the HDMI cable that connects to the TV.
To answer your other questions, I used some styling cues from my Sony Walkman Pro, and that's where the tiny switches came from. The PLAY and STOP buttons simply turn the power on and off. I had thought about adding an eject function to the STOP button, but that made the mechanical design a bit too complex. And finally, I still want to add some kind of logo, and some lettering around the buttons that indicate their functions. I'm leaning towards dry transfer, but I'm not sure how well that will work on 3D printed material. It's on my to do list.
Anyway I am curious what types of scaling options your Atari has. Can you use integer pixel ratios or does it use bilinear or other scaling methods with the triple buffering? I'm a bit concerned about the buffer creating lag but I don't see a good solution to fix this in the event scanlines go over. Halting or speeding up CPU execution to lock framerate might have implications on audio bending or other artifacts as well as inaccurate paddle timing.
The 2600 core timing is always running at the exact rate of the original Atari hardware. I'm using a triple buffer to frame sync the 2600 video timing to the output video timing, and the horinzontal scaling is always an integer multiple of the 2600 horizontal resolution. The vertical scaling, on the other hand, uses what's called a polyphase interpolating filter to scale from 208 or 224 lines, user selectable, up to the output resolution which can be 480, 600, 720, 768, 1080, or 1200 lines.
One day I might experiment with trying to V lock the output timing to the 2600 timing, but for right now the delay through the triple buffer doesn't bother me.