I'm not in Bangkok but just got mine done to my Toyota Vios and it was 4,500baht . I think it's a common price all across Thailand .. my wife called a few places around the area and all said the same
If you have your TR visa approved already you will be stamped in with that first if the visa is in your passport.. if you have a E-visa well then you don't need to show but after the 30 days you would have to leave and come back in and show the E-visa to be stamped in for 60 days