This is really an appointment+ and marketpress issue. I have an appointment + scheduler which you can view at https://unionsquaredogwalker.com/store/products/appointment/
With Hakan's help I made modifications to functions.php so that off hours (8-10am and anytime after 6pm) cost more. This cost correctly shows up in Appointment +, but when a user goes to the checkout the cost that shows up is the non off hours (cheaper) cost.
Steps To reproduce
1)Go to https://unionsquaredogwalker.com/store/products/appointment/
2) Select 30 minute dog walk
3) Select 8-10pm
4)Confirm price is 22 usd
5)Fill in form and click "Please click here to confirm appointment"
6)Click Buy Now
7) You will be redirected to shopping cart and the price will read 17 dollars, instead of 22 dollars.
Therefore, somewhere along the line the price is being reverted to the product price for non off hours.