I like Whitewolf's formula, but since the 125K stack is at the table, I would qualitatively argue that fair value is a bit less than $90. Some one smarter than me may be able to calculate it. 50/50 sounds cheap since you're essentially selling the seat for half price at $45.

I would offer some point (or give your friend the option) on a sliding scale between 70/30(you/him) and $70, with $10 = 10%. You're giving up a smaller discount (selling at a $63-70) and he's getting a good price into the tournament.