Upsells Cap

It would be great if there was a place to cap the total cost of a per night upsell. For example we charge $8 per night for a crib but up to a maximum of $40 per stay. Right now I have to create 2 upsells for the same item (one per night and the other per reservation) and instruct guest that if they stay more than XX nights they are better off with the per reservation option. It is confusing for guests.