Where can I get a quick and affordable PCR test in Koh Samui before my flight back to Toronto?

Hello all! We are in Koh Samui at the moment and are going back home on the 18th at 7:40 pm. So, we need to do a pcr test within 72 hrs. We would depart here 17th 7:40 am in Toronto time and land there the 19th at 4pm. I assume then to do our test on the 16th around 4pm (Toronto time) - which means 17th here at 4am. Since our flight is the next day, I’m looking for somewhere that provide fast results over email and not too expensive?

Thanks a lot guys!