It’s free if it’s issued by the immigration office on the 2nd floor and takes abt 2 weeks time to get it.
In the past, if you wanted to get it within 3 working days. There was an agency down there (next to a photocopy shop) who managed this to you at 500 baht.
But after April 2018, the new agency at the same office place charges you 1,000 baht and you will get it the next day after 3 p.m.