@Doree ********
, calm down take a breath.
You're not going to have any problem waiting until the last day on your extension before you bounce out of the country. It costs 500 baht to get stamped in and out of burma at Mae Sai.
The Mae Sai - Tachiliek border with burma will NOT ask you for proof of funds, proof of onward travel or proof of a hotel booking when you bounce out and back in there
You'll get a 30 day visa exempt entry from that border and you can extend it by 30 days more at the immigration office like you did before for 1900baht.