Javascript dates and prices: I need help with CODING!

I am having so much trouble with this and it is now affecting my business. Wix support told me take certain steps which i did however I know nothing about code and I cannot get it work for the life of me!
I feel what i need is simple;
I have 2 date pickers…so…
‘date 2’ - ‘date 1’ = ‘a certain amount of days’
‘a certain amount of days’ will then autopick from the radio menu the price which is applicable.

hheeelllpppp.

Please elaborate more.
How do look like your Radio-Menu ?
Screenshots of your SETUP ?