Before spending any money, you should sit down with an attorney to see if your fiance will be admissible or not. For example, if he ever said he is a U.S. citizen or has had any criminal problems, he might not be admissible at all.
If he was here for more than 6 months before he had voluntary departure, then he will have at least a 3 year bar (possibly a ten year bar if he was here for more than 1 year) and will need a waiver. This waiver must prove that if he is not approved, it will cause you extreme hardship.
Typically a fiance visa will get him here a little bit quicker (assuming he is approved) than if you marry him and then petition for him. But if he needs a waiver, it will need to be approved before he can come here.
I recommend finding an attorney who is experienced with this type of case to help you review his options as well as to assess his chances at being approved for a waiver.