There is no fee for annulments. It is not based on ability to pay. Do try to keep up.
You are, of course, correct. What others do not understand, but Catholics do, is that marriage is not merely a simple ceremony but is instead one of the seven holy Sacrament gifted to us by God. And as with all Sacraments, one has to be worthy of receiving it. If a Catholic enters the Sacrament of marriage for all the wrong reasons or otherwise prove they were unworthy of receiving it to begin with then the marriage is invalid. That's what they don't understand and instead allow their bigotry against Catholics full rein.
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How much does it cost?
Pope Francis has asked dioceses whenever possible to provide their tribunal services free of charge. Depending upon how much your diocese is able to subsidize the work of its tribunal, you may be asked to pay a nominal fee. You may also be asked to make a donation following the completion of your case. Fees are typically payable over time, and may be reduced or even waived in cases of financial difficulty. Other expenses may be incurred when consultation with medical, psychological, or other experts is needed, or if you obtain the services of a private canon lawyer to represent you.
http://www.usccb.org/issues-and-action/marriage-and-family/marriage/annulment/index.cfm
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Please try to keep up.