It is unlikely that a unit can be built one-off cheaper than buying a commercial unit that is likely to work:
imho it can. the major cost will be the power fets.
The semiconductors are one of the least expensive parts of a product.
Semis are cheap as sand. Well, good quality sand. Not that shitty beach stuff.
The most expensive part of such a project is the months long development cycle, equivalent to thousands of dollars of labor you could've earned at McDonalds* in the same time. Tens of thousands, if you wind up needing multiple cycles of refinement, versus, say, the same time at a technician-level job in most fields.
*Not counting the labor cost equivalent of voluntarily crushing one's soul, mind.
That's a lot of beer!
For example, you'll easily spend $50 on the heatsink, let alone on machining it, and the labor of mounting components to it. The capacitors alone will probably be more; this is certainly true at higher voltages, but I'm not sure offhand if it's quite as true at low voltage. 300A worth of 1210 ceramic chips is quite a lot of ceramic, though, and those babies don't come cheap, nearing a buck each. It racks up fast.
And that's to say nothing of everything else; the control circuit will soak up $50 of chips, and assorted resistors capacitors, LEDs and so on, easily. Maybe you'll choose to begin development on a $20 to $200 dev kit first, using anything from a cheap MCU to a fancy FPGA.
Sheesh, I already spent two or three transistors's worth just writing this post. I need to make this a business, telling people how they're wrong.
This is really all just to say: the economics of one-offs is vastly different from production.
On a project like this, you're mostly paying, in labor, for the experience of having designed and/or completed the thing. In that case, you're making an investment. You might as well put that knowledge to good use by obtaining a more lucrative job.
Tim
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