How much would it cost to get my record expunged?

Most likely $125, plus if you pay an attorney to do it for you whatever that costs:

§ 15A‑145. A person who files a petition for expunction of a criminal record under this section must pay the clerk of superior court a fee of one hundred twenty‑five dollars ($125.00) at the time the petition is filed. Fees collected under this subsection shall be deposited in the General Fund. This subsection does not apply to petitions filed by an indigent.

Although I do not practice law in the State of North Carolina, here are my initial impressions.  The general rule is that you cannot pay for a record to be expunged.  There is no fee associated with it that takes care of the entire process.  However, since you state that you have been charged with a crime, it is possible that you can prevent yourself from getting a record if you can resolve this pending charge favorably.  I suggest that you spend your money on an attorney in the interest of keeping your record clean.  Good luck.