Unrelated business income tax is imposed on net earnings from a trade or business regularly carried on that is unrelated to the charitable purpose for which a charity is recognized as exempt.  Normally, healthcare services are considered charitable at the federal level, even to fully paying customers, but you should be sure that you are not exempt only for providing free services.  If so, expand your purpose. (See Ready Reference Page:  “Nonprofits Often Worry About UBIT”)

Your scheme to ask payors to make a “donation” in return for a hearing aid won’t work as a means of giving deductibility for a major portion of the payment.  The basic rule for “quid pro quo” gifts is that a payor may take a deduction only to the extent that the payor gives more to the charity than the value of what he or she receives in return.  Public TV stations sometimes allow a full deduction if they give certain low cost souvenir type items, but many of the contribution deductions are reduced by the value of more substantial items the stations use as premiums for gifts.  The key issue is the value of the items received in return, not the cost of those items to the charity.  You can readily determine how much the hearing aids would sell for if provided by another nonprofit or commercial organization.  Only the amount paid in excess of the fair market value would be a gift.  (See Ready Reference Page:  “Charities Must Set Value on ‘Quid Pro Quo’ Gifts”)  But why would people pay more for your hearing aids than they could pay somewhere else?

For those who can pay the full value, charge the value.  You can ask them for a legitimate contribution to help support others.