Anonymous participant oh, lol, no. It's 10k for sending the initial application.
Extensions done in Thailand are 1900 like the others. But it's currently recommended to just travel out and back in for a new stamp, due to the document-checks if extension is done in country.
It's either $30,000 as a lump sum OR $2,500 a month. Not both.
I'd go with the monthly income, get a bank account when you hit the ground in Thailand, and start transfer at least the minimum monthly required for the extension.
You'll have plenty of time to get that sorted with the Non-OA visa, but it doesn't hurt to start early.