I'm 99% positive there are entire companies dedicated to financing the tax bill for these types of taxes, just to get a cut of the equity.

EDIT: See https://www.esofund.com/ There are other newer places also like https://join.equitybee.com/

Also, brokers who create a secondary market for this equity will also arrange financing, but it depends on the "hotness" of the equity.

SIDE NOTE: If you have SpaceX stock, and you're going to leave it on the table due to taxes, reach out to me and I can arrange for something also. But go to ESOFund, etc first of course - those are professional outfits.

Can you point to some example(s) of companies that finance exercising private company options?

I edited my original post. See https://www.esofund.com/ There are other newer places also like https://join.equitybee.com/

Thanks!

how much was the 409a valuation in 2017? $2-$3 a share? 15000 at $3 is $45K. assume all profit, lets say between federal and state he had to pay 40% on that (assuming its not long term capital gains, might very well be, and he's in a high tax state and has a high yearly income). so he would have to pay another 18k at most on top of the few thousand to excercise his options). though possibly less, as I said about long term gains.

18k isn't a small chunk of change, but it should be managable by most engineers. going from 4000 (.27*15k) to 20+K is a big jump, but it shoudn't be what scares you away.