GURPS Magic makes some assumptions about enchanters and their wages which I find questionable, resulting in a rather sudden leap from cheap enchantments to expensive ones. Enchanters are assumed to either be skill-15 journeymen who earn average wages or masters who earn comfortable wages, typically with skill 20. All of them have Recover Energy at 15.
While an average wage might be just about reasonable for a journeyman, I find the idea of skill-20 masters only earning a comfortable wage hard to swallow. It seems to me that there would probably be a range of skill levels among masters, providing a range of enchantments at different prices per energy point. After a few hours messing around with spreadsheets, I came up with a few numbers which seem a bit more plausible to me and smooth off the price curve.
A skill-16 comfortable master with one (average wealth) assistant, both with Recover Energy-15, can enchant items up to 20 power, for a price per point of 0.0016 times typical monthly pay at his TL.
A skill-18 wealthy master with three assistants, all with Recover Energy-15, can enchant items up to 40 power, for a price per point of 0.0022 times typical monthly pay at his TL.
A skill-21 very wealthy master with Recover Energy-20, and two shifts of six assistants can enchant items up to 70 power, for a price per point of 0.0036 times typical monthly pay at his TL.
A skill-25 filthy rich master with Recover Energy-20, and two shifts of ten assistants can enchant items up to 110 power, for a price per point of 0.0151 times typical monthly pay at his TL.
All those numbers include the usual assumption of every mage being able to spend 10 energy per casting. I tried messing around with things like not having the master use his energy and using paut to recover faster, but none of them resulted in savings. I also assume that there is no practical way to exploit Raise Cone of Power or other tricks to draw massive amounts of energy from unskilled mundane assistants.