That is up to the church. The church must set a "fair market value" for the niche. That might include such things as the value of the property, the cost of perpetual maintenance, and so on. If your payment is more than the fair market value, that difference can be taken as a donation. If any part of the payment is considered a donation, the church is required to issue you a letter, receipt or statement that specifies the amount of the payment, the fair market value, and the allowable tax deductible donation.
