No charge, just go to the immigration office in whatever city you’re in. Fill out a TM47 (one page document telling them when you arrived and where you’re living). You’ll need your passport, copy of your visa, and TM30.
we went through a realty company (Cornerstone in Pattaya) to rent our condo so we worked directly with them and they worked with the Thai landlord. We just needed to show our passports and visa.