I'd teach AP Chemistry. It's useful for teaching AP Biology too. The equipment, with some application-specific packaging and instructions, might also work for: aquarium keepers, gardeners, pool owners, beer brewers, people on well water.
Full DIY builds are cheap for a colorimeter, photometer, and turbidimeter. One can make all three for about $30, not counting labor and a computer.
The trouble is manufacturing volume. Sadly, not every student takes AP Chemistry. I realize that the manufacturing processes with low per-unit cost (casting, forging, blow molding, extrusion...) all have high set-up costs. This really is my complaint: if people cared about learning science as much as they cared about pointless toys, the production volume would let us have these things at prices ranging from a few dollars (simple colorimeter) to a hundred dollars (stuff with decent lenses and moving parts). The affordability of low-end cell phones makes it clear how low prices could go. I know you're having trouble due to the costs associated with low volume, but to an ordinary purchaser your price looks like a rip-off.
FYI, there are about 320000 people learning AP Chemistry, of which about 9600 are homeschooled and thus unlikely to reuse equipment from prior years. Assuming the equipment in schools needs replacement every 20 years, perhaps 25000 could be sold per year if the price were low enough to not be a budget problem. I'm thinking you'd have to knock about 90% off the price, and I suspect that 25000 per year is nowhere near the volume you'd need to justify the set-up costs of high-volume manufacturing processes. I may be wrong though... maybe you can get a good deal on plastic molds or custom aluminum extrusion dies or molds for some sort of casting process.