Can I extend my 30-day visa exemption in Thailand and what are the cash requirements upon entry?

Sawadee Kha, I want to come from Indonesia to Thailand in October for about 45 days. I have a French passport.

1/ Is it true that the 30 days visa exemption (stamp for free on arrival) can be extended one time for 30 days (1900 bahts?) at the immigration office? Because in Bali, you can't extend the "free visa" as it is not a visa.

2/ I read that even for this tourist permission of stay you have to show cash if asked. Is it true? And I read different amounts on different websites : some say 10000 for single people or 20000 for a family. Others say is 20000 even for single people. Where I can find a 100% certain information?

Thanks in advance for your help (please only reply if you really know the current rules, not only assuming or speaking about your experience 2 years ago).