Learn English – Difference between “Simultaneously”, “Concurrently”, and “At the same time”

Reasonable means that whatever decision was made is appropriate given the particular circumstances, and most would regard it as so.

Justified means that whatever decision was made is done for a good reason, in the interest of fairness.

There are times the words could be used interchangeably, and contexts where the difference is subtle. It all depends on the nature of the request or issue at hand.

I might use "justified" if I was angry about something, and was acting in response:

Was it polite to skip their wedding after they insulted me like that? No, but I think my decision was justified.

I might use "reasonable" if I think everyone would agree that there was nothing else that could be done:

Was I happy about missing their wedding so that I could go to my mother's funeral? No, but I think my decision was reasonable.

But there are contexts where either word will work just fine:

You said that you'd deliver the cake before noon, but it didn't get here until 3 o'clock. I think my request for a refund is reasonable/justified.

In that sentence, reasonable would work because most people would agree that a refund would be appropriate given the circumstances, and justified would work because the request is fair.

They are equivalent enough in general usage that, in the context you have provided, it doesn't make a difference worth worrying about.

As justification for that:

You would ordinarily use price for an item or product that could be purchased. This isn't necessarily physical. The customer can buy airtime for instance, and therefore price works in your example.

On the other hand, fee usually indicates payment for a service. This could be a consultation with a doctor or payments to the tennis club for using the court each week. In your example your service is the placement and display of the banners, so fee works too.