I gave this some thought today, and figured out the ampacity of various trace widths and copper thicknesses, and came to the conclusion that if you were willing to do the work yourself, you could get reasonable ampacities from a relatively inexpensive board - but you're limitted in size.
Later, I realized something: When you pay your money, what you want is copper, and lots of it. You don't want to pay for fiberglass and glue, just copper. A square foot of double-sided PCB runs something like $25 or $30, and you're only talking about one to four ounces of copper... and then you're going to etch most of that away. In the end, you'll end up less than a half of an ounce of copper... that's pretty expensive.
Think of how much copper wire that amount of money would buy... or on the other side, how much less it would cost to buy that amount of copper wire.
One advantage is the very narrow air gap... but with a little ingenuity, I think you could get the same thickness with wire of a similar ampacity.
That's not to say that they aren't cool... they are. Cool enough that maybe I'll fiddle around with them. But a half pound of 22 gauge wire would give you more bang for your buck, I think.
