Different product prices per line item options
If I understand what you're trying to do here correctly, you may need to create some custom Rules.

Event:  Calculating sell price of product.

Conditions:  This is where it gets tricky.  If the date range is not on the product entity, you'll need a way to get the values from the product display node, that could be annoying in and of itself.
Now, if pricing for date ranges are statically calculated (ie: a 3 day trip ALWAYS adds $50), you could set up some custom code to dynamically do things like that.
On the flip side, if those range rates are different per product, it seems it would be necessary to define those on the product entity.  And furthermore, you would probably need to create products for each variation (as in, variation for every combination of departure city AND date range).

Action:  Add amount to product price (or something like that, I'm not looking at Rules directly).