@bombastinator, some places have them around $50. So, not absolutely ridiculous.
I've even seen them at around $80.
Got a few Sxmini SL Class YiHi SX485J mods in the collection as they're a decent 21700 mod. TC on them is very good, you just have to use Joules the same as Watts. So if you need to use 30 Watts for the coil, you use 30 Joules.
But I can certainly recommend YiHi mods, especially if you find them at a good price.