What is the best border for activating a tourist visa when leaving Koh Phangan?

@Yoga ************

you could first get a 30-days touristic extension for 1900.- THB on Immigration, before you do the border run to activate the 60-days tourist visa.

In Case you want to avoid doing a 1900.- THB 30-days extension, you may do the border run to activate your 60-days Tourist visa, however then you need to wait until the very last days before your 30 days stay permit expires, in order to get a close to 90 days total stay permit without having to apply for an extension on Immigration.

Means: If your total stay does not exceed 90 days, you might do as well so without a 30-days extension for 1900.- THB

However I would say, if your plan is to stay 90 days plus a few days longer, then go the first route: get the 30 days extension on Immigration for the 1900.- THB, and before the total of the 60 days are over, do the “border run” and activate the Tourist Visa

KEEP IN MIND: your 60 days tourist visa has a validity for use for an entry, of three months starting from the date of issue (stated as in "visa must be used by" and the date). So you are good to stay for 59 days before you exit Thailand and still have around 30 days left to activate the 60 days Tourist Visa

The border run options are via Ranong/Kawthoung to Myanmar, or to Perlis/Satun at the Malaysian border. A border run will cost you somewhat around 4000.- to 5000.- THB, from Ko Samui or Ko Phangan, not including the ferry from the mainland to the islands.

Alternatively you could fly from USM Ko Samui to Singapore and complete a border bounce on Changi airport, or even stay in Singapore for a few days before flying back to Samui.

The costs for this border run by air, would be around the same you will have to pay for the minivan tours to the land borders