Let users defer or opt out of payments

For a government service we have to collect a service fee. The amount is in the tens of dollars but as this is a vital government service the fee can be differed or waved. If this happens our client has to eat the cost, so this is not a preferred outcome. There is no guideline for payment exemption.

Currently this is done in person, so the option to not pay is not presented unless the person states that this would be difficult for them. In a way it's like going to a museum with a suggested donation. Most people will pay it.

As we switch open to online the social pressure seems to be much less. If users are given a clear choice "would you like to pay for this or get it for free" it seems like most people would just pick free, like using WinRar

The initial thought is to hide the payment waver in the small text on the page. Unfortunately I feel like this would have the opposite of the desired effect. The link would be found by well educated people, but non English speakers and other vulnerable population groups would miss the option.

What is a good way to set up the UI to allow people to opt out of paying, but strongly encourage those who can to pay?