That's a common way to save on taxes by paying a bit upfront. It's usually not done at such a late stage because of the cost when the strike price is high. It's more common in pre-A or at least pre-B companies when the strike price is smaller.

I certainly wouldn't drop 100k unless they offer a commensurate signups bonus (the 100k goes to the company so they could give you a bonus of $100k if you exercise the options which should help, though you'd still be on the hook for the taxes on that bonus).