So whether it's $4 per signal direct from wehonest or even double that on eBay, isn't the elephant in the corner the cost of the electronics to make the 3 LEDs "work"? There's a camp that wants manual control using 3-position toggles (apparently about $4 for the control) and another camp that wants prototypical signaling with "daisy-chained" block detectors (cost all over the map depending on features).
But my guess is the biggest camp is what's offered in off-the-shelf 3-aspect heads with timed-yellow-to-green behavior. In this case the board shown earlier by GRJ seems like a capable no-soldering-required solution but comes in at about $12-$18 per signal head. In other words several times the cost of the signal head itself!
Just my opinion but isn't this where the focus should be?! Has someone shown how to hook up this board for 3-rail using the isolated-rail method? I see this board takes AC or DC voltage but, again, has someone confirm the "grounding" of the commons works when using Accessory AC from an O-gauge train transformer? Etc.
I can imagine cobbling together some eBay relay modules and timer modules to perform the timed-yellow-green behavior using an insulated outer rail trigger. I'm guessing less than $5 per signal head. Not sure if there's any interest in this or if I'm completely missing the boat on what guys are after.