Do South African travelers need 20,000 THB in cash for a tourist visa on arrival in Thailand?

Good day

I am from South Africa. I am planning to travel to Thailand over December and January for about 21 days. Apparently there is a thing where South Africans need to have 20000THB in cash to get a visa.

Is this just a rumor or is it something that is true? Is there any other important requirements for me to get a tourist visa on arrival?

Please keep in mind that I have NO INTENTIONS of staying or working in Thailand. This is a holiday only and I will arrive in Bangkok on 19 December 2019 and will leave from Bangkok on 9 January 2020. I will have domestic flights, but will NEVER leave Thailand within the above mentioned dates.

Thank you in advance for your help.