The filing fee is Dallas is $255.00. The address of the Court is 600 Commerce Street, Dallas, Texas 75202. However, you cannot just show up and file your divorce. You have to prepare the proper paperwork.
You can either retain an attorney to handle your case (most expensive); prepare the documents yourself (cheapest, but requires a lot of work); or have the forms created for you by an attorney but represent yourself (less expensive and much less of a hassle).
Good luck!