What are the requirements for re-entering Thailand on a visa-exempt entry?

The rules are clear and known by the OP. Discussion of the rules are crazy rules and should be handled different on your statement about hours or days of stay, is a total different discussion and this is not the place for it. We are just guests in this country and we have no influence on their laws. Success to all.

Hello I am arriving in Don Mueang in July on a 2 day visit from Vietnam, I will have a return flight and a hotel booking, my question is will I still need baht in cash? It seems quite a lot for such a short time in Thailand.

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

It can be from anywhere and you can show funds from your country then when you arrive you must go to immigration and do a TM 30 report you got a day or two to do this if your landlord doesn’t do it for you it’s a must now if you want to extend for an extra 30 days

Proof of funds should be 10k for a visa exempt entry

I guess you mean you arrive using the Visa Exempt Entry, not a Visa on Arrival (this one you buy at the airport before Immigration). You can use an onward ticket from anywhere in Thailand outbound.