Are your in Thailand? If so get letter from the bank confirming the 800k and bring a 1yr lease agreement and a couple of passport photos and copies of your passport pages. Take all to immigration. Might be best to go to immigration in advance and get their document checklist.
If not in Thailand, use evisa system to apply. Then deposit the 800k when you get here.
You will need to deposit 800k in your Thai bank account and apply for your non-o visa. Then, for your 2nd extension you can show 12 consecutive 65k deposits into that account. After your 2nd extension is approved, you can spend your 800k. Not sure why you're frustrated, it's just the rules of how it works.