Make the most exciting roller coaster you can without it being too exciting (I'd say MAXIMUM about 9.99), or just find a good exciting pre-made roller coaster.
Then... Round the intensity rating to the nearest 0.1... Meaning if you have a number like 9.94, 9.93, 9.92, 9.91, it would be 9.90. If it was 9.95 and up, you would make it 10.00.
Make that number it's entry price.
Yep. If your number was 10.00 (NOTE: Those were only examples, not REQUIRED), then its price would be $10.00. They will never complain about it being too expensive. I did 'Dark Age - Robin Hood' with 2 roller coasters, including the pre-built one.
Although if its a low intensity rating, don't bother really.

IMPORTANT NOTE: This only works with roller coasters or rides built on track. Things like 'Enterprise' and other exciting 'smaller' rides, all those sorts of rides don't count... And they won't go on it if you try.