What is the cheapest and fastest way to do a border run in Thailand when on a 30-day arrival visa?

I guess you'll get a 30 day visa exemption. I'm not an expert in this as I'm on an METV so it's different. So others may be able to confirm!

Yes, dead easy. I found it more straightforward to book the bus tickets at the bus station as I somehow managed to buy the wrong ones online!

As previous posters suggest, you get off the bus at Mai Sai bus station and jump in a Songtaew to the border (takes about 15 mins). Then you walk through and get your exit stamp from Thailand. Keep walking (cross over the bridge) and you go into a little office on the Myanmar side where they take your passport and give you a receipt, in exchange for a PRISTINE $10 bill, or 500 bhat. You then wander off into the market if that's what you want to do.

When done, go to the opposite side of the bridge and pick up your passport from the Myanmar chaps, cross back over the bridge diagonally and you get to the Thai border. Fill out your forms, get stamped in, then look for the Songtaew to take you back to the bus station.

I couldn't find anything I wanted to eat at Mai Sai bus station, so worth getting something by the border. I survived the day on pringles and haribo, which isn't recommended 😂