A buddy and I go on a trip every year, share a room, and split the cost. This year, I will use my hotel points to pay for the entire cost of the room. Is it fair to ask him to pay me for his half of the room, and if so, how much?

Here are some details:

10 night stay. The room in question, if we paid cash, would probably cost about $300/night, or about $3400 after taxes for the trip. But if we were paying cash, we wouldn't stay at that property. We'd probably stay at a less nice place for about $150/night, or try to Priceline something for about $100 or so.

Instead, I am using 56,000 Starpoints. Most of these came from hotel stays and credit card spend, but some, I essentially "paid" for, for example, paying a convenience fee to pay my taxes with the credit card to get the points.

So what is fair and reasonable?

Half of the $300/night that the room would cost?
Half of the $100/night that we'd pay, otherwise, for a lesser hotel by Priceline deal?
Half of just the amount that I can trace to having "paid" for the points?
Nothing?

I'm thinking half of the $100/night seems fair to me, but what do you all think?