Assuming a judge grants the expungement, a lawyer will cost you $3k-$5k to work through the process.
Part of the money likely makes its way into the district attorney's pockets either via an election donation or some other method. Why? Because, having a letter of support from the DA's office makes it easier for the judge to approve it.
There's also a huge caveat to this whole process. Your expungement is only good for the state in which you were charged and filed the expungement. Your record will be "clean" in that state only.
Since information travels instantly through the interwebs, federal agencies and other states will still have your records on file and will not expunge them unless you pay even more money for the attorney to make those requests.
It's just like your personal videos JJ. Once they are out there, its impossible to erase them completely.