What's a good deal?

[Tokyo!!]

I play in a weekly $30 buy-in tournament league where your finishes accumulate points (as well as cashing for top places etc.). Each week, a small amount of money from the buy-ins is taken out and put to the side for the championship game. The top point getters and those who have won at least one tournament that are also not in the top 9 are freerolled into the championship event. I made it in, but am unable to play due to school reasons. It's been cleared that my friend can play for me who didn't make it into the championship event. I'm having trouble coming up with a reasonable fair deal for splitting any money he makes or having him just pay me for the seat and a small percentage of winnings. My friend is an above average player who was gone for most of this season, which is why he didn't qualify. He has played with these people a fair amount and took 2nd in the championship 2 seasons ago. Any ideas on a fair way to do this?

Relevant info: There are 16 total players for the championship, 2 tables of 8. The top 4 pay, with likely payouts of $700, $450, $200, $100 (unless a seperate deal is made at the table). The starting stacks at my table are as follows, Hero: 50k, then 125k, 75k, 45k, 25k, 25k, 20k. The other table has stacks of 115k, 90k, 80k, 50k, 30k, 25k, 25k, 20k. The blind structure is set for a deep-stacked tournament, with 30 minute levels and starting blinds of 100/200, then 200/400, 400/800, 600/1200, 800/1600, etc. etc.

[FatMan]

Without him playing for you, your take would be $0. So anything he wins for you is a bonus. Split it with him 50/50 or at least 60/40.

[WhiteWolf]

The most straightforward way to handle this it to have him pay for the seat. The fair amount would be (Total Prize Pool) / (Number of Players). If you do this, I don't see any justification for taking a share of his winnings, as he is giving you the full fair value for your seat.

Edit: I missed the fact that the starting stack sizes will be different (this seems like a very odd structure). This obviously makes it harder to assign a fair value for the seat. Perhaps take the above formula and multiply it by (His Stack Size) / (Average Stack Size). Or just do the 50/50 split to make it easy.

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.

how many buy-ins you played before getting to the championship??