A Few Points To Consider
Price and availability may be a great way to choose a rental car, but they should not be top priorities in choosing a clergyman to officiate your wedding. Personality, creative abilities, ceremony flexibility, experience, dependability, integrity, and other factors are really more important. A great officiant is a bargain at $600 and a bad officiant is expensive at $5.00.
Pastors and Priests have salaries and congregations. The congregation is their "marketing plan". They do not have to advertise. Therefore, their honorariums are not comparable to the fee of a full time wedding minister. Also, a pastor or priest has restrictions placed upon them by their church, so there is usually very little flexibility in the ceremony.
Then, there are "script readers". This kind of officiant has very little spiritual and emotional involvement in the ceremony. This can describe a judge, some clergymen, and many professional officiants who got ordained on the Internet to make money doing weddings. By the way, while this kind of ordination is considered legal by the government, it is spiritually fraudulent.
Pennsylvania Marriage Law stipulates that any minister officiating a wedding must be ordained by a congregation. Internet ordinations circumvent the intent of the law, but for some reason the state is not enforcing the law. In the same way, a civil ceremony is to be officiated by a judge, mayor or clerk of courts, not a minister. Again, the law is not being enforced.
In any case, the major factor in officiant fees is the cost of advertising. You want an officiant for your Big Day when you need them. And, you want to find them with relative ease. Therefore, part of what you are paying is for that presence in a variety of advertising media.