Is it cheaper to cross into Myanmar or Laos for a border run in Thailand?

Then just come in, get the 30 day visa exempt entry and get a 30 day extension on that from the immigration office that serves where ever it is you're staying that'll give you 60 days total.

IF you need more time, go to a border, stamp out of thailand, stamp in and out of another country and back into thailand to get a NEW 30 day visa exempt entry,

Keep in mind you're allowed TWO 30 day visa exempt entries by land in a calendar year (Jan 1 - Dec 31) so if you come in visa exempt by land from Cambodia, that's ONE, meaning you could bounce out and back in by land ONCE more next year for a new 30 day visa exempt entry

OR

You could get a tourist visa from the thai consulate in Phnom Penh before you come here and that'd stamp you in for 60 days when you enter and you could get a 30 day extension on that at the immigration office for 1900baht

WHERE in the country are you?