It varies from state to state. There are different qualifying thresholds to get over. There are things that disentitle you to compensation. For instance, in some states, if you have a felony that's totally unrelated to the wrongful conviction, that disentitles you to any compensation at all.
There are statutes of limitations that are in place, which are incredibly difficult, so once you're exonerated, you have a period of time to bring your action for compensation. Again, for most people who are released from imprisonment, their first priority is to get food on the table and get a roof over their head, so the passage of time often takes place and they lose the right to seek compensation. That's important to keep in mind.
Of course, the amounts are all different. Again, as I said, there are some that are very miserly, and some that aren't so bad.