Let's sort out how the proof of funds works
There are two instances where you could be asked for it.
One is at a thai consulate buying a visa for thailand. In that instance you show a bank account to meet the requirement. It can be a thai or foreign country account. You CANNOT show cash :/
The other instance when you can be asked for proof of funds is when you stamp into the country. In this instance it HAS to be in CASH. You cannot show a bank account. :/
Keep in mind you can be asked for proof of funds when entering on a visa exempt entry, a tourist visa or even a Non-Immigrant visa. You will NOT be asked for proof of funds on yearly extensions of stays.
The actual law is as
@Ll***
stated entering visa exempt it is 10K baht (or the equivalent) in cash. BUT when people are asked for proof of funds stamping into the country at both Suvarnabhumi and Don Mueang airports they are asked for 20K baht (or the equivalent).
It is really 10K baht for visa exempt or visa on arrival
20K baht for tourist or Non-Immigrant type visas