if only count the total of the raw material, my cost is low
the regulator price is pretty open, you have to be lucky to pick up a nice one for low price, majority is around $50-$100.
the good solenoid, and the good metering valve, with good price, most of the time, are pure luck.
started from last couple month, there were the Burkert 2822 and the Parker Hannifin H3L, really good parts/deals both showed up at the same time. put the msg out there so everyone would have a chance to get them, an opportunity that won't show up again in years..
now the burkert 2822 are gone, it will be hard to find a good solenoid and cost will go up.
Still have enough good solenoids to build,