There are a couple of common misunderstandings regarding marriage in the church that I think needs to be addressed. Perhaps this could be a "sticky"
-A Catholic is bound by canonical form in their marriage. This usually means marrying in a Catholic parish, and going through the usual preparation requirements. Sometimes a Catholic can get a dispensation from form to marry in another location, but they are NOT dispensed from the same requirements of preparation.
A Catholic must get permission to marry a non-Catholic Christian from the Bishop, even if marrying according to form in the church.
A Catholic must get a dispensation to marry a Non-baptized person from the Bishop even if marrying according to form in the church.
Both of these are usually taken care of by the priest, sometimes without the couple even knowing about it.
--A Non-catholic is not bound by these same canons in their marriage. They can marry just as validly in a church or by a jp. The church regards non-Catholic marriages valid until proven otherwise.
The necessary parts for a valid marriage are: "Free, total, faithful, and fruitful". This is for both Catholics and Non-catholics. There are many nuances to these terms that cannot be explained here. A Civil divorce does not undo a valid marriage.
--If someone wants the tribunal to investigate a marriage for validity, they are asked to pay a fee to cover some of the costs. Usually, it only covers about half of the costs for the completion. Investigations take canon lawyers, and a tribunal court. There are actual costs involved. It is not considered a "donation" in paying this fee. You cannot "buy" an annulment. If there are financial difficulties, no one is denied the investigation process based on this.
There are 2 (sometimes considered 3) kinds of categories under the umbrella of "annulment". Technically, this term is used for those who are presumed to be in a valid marriage and must go through the full tribunal investigation and process with questions to answer as well as needing witnesses. This term is also known as "Declaration of nullity". The church CANNOT "annul" a marriage. It can investigate it to see if it was valid at the time of vows-- to see if all of the parts were in place.
The other category, called "defect of form" or "lack of form". This is when a Catholic marries outside of the form of Catholic marriage with no dispensation to do so. This is a relatively quick process involving paperwork and not a big cost, but still must be done.
A 3rd "category" is ligamen. This is when someone attempts a marriage, but was still presumably validly married to someone else. (This is NOT involving civil marriage/divorce).
A person simply is not free to marry when they have made vows to someone else, and that marriage has not been declared null.