How much cost to expunge the case (papers from the court) if your case dismissed? should i pay my lawyer?

I had a court, judge pronounced me not guilty! Now my lawyer tells me that i have to pay few thousands dollars to expunge all those papers from the court. Do i have to pay for that? even if my case is dismissed already... ? I always thought that i have to pay and wait few years to expunge my case by the judge, but only if im pronounced guilty, but I'm not. The cort said my case dismissed. In order to have clean record, should i pay to my lawyer? or is it already automatically clean since the day i was pronounced not guilty?