500k baht is 41k per month for a year. They need to make sure you can support yourself with CASH or equivalent. This is a normal requirement for most countries visas and investments like stocks/crypto aren't cash. You could try borrowing against your stock and deposit 500k in savings.
Write a letter that explains why you want the visa and how you meet the qualifications. You need to convince the Consulate reviewing your application why they should approve it.
I'm paying AIS 200b for 50GB 15Mpbs / mo. Goto an AIS store in the mall and see what they have. They will push an expensive unlimited plan on you, but if you don't need it, get service for 200b to 300b.
Tell immigration at the airport that you couldn't wait for the DTV and slip a 1000 baht note with your passport, wink at them and ask if there's anyway they can stamp you in for 6 months.😉