From what I've seen the common way to make payments is from your thai bank account with a qr code. Don't know if foreigners are allowed to do this or not.
If you have the 800,000 just do it yourself at a cost of 1900 baht. I can understand using an agent if you don't want to keep the large sum tied up. But otherwise like I say just do it yourself.
I've not asked directly. I am just reading off the handout. I suppose for what it costs I just as well copy all pages and if not needed then no great loss.
just wondered as when I booked my flight they had a free travel insurance scheme going which covered the whole length of the trip which was handy as I was coming for 3 months. This was stopped at the end of December. But because I had paid for my flights before the cut off date they still honored the insurance even though my flight wasn't until the end of January. As I say that's how it was with the old scheme, I have no idea what the new scheme is. But certainly worth double checking.
If you have booked and fully paid for the flight before the cut off date of 31st of March I would have thought it would still be valid for your travel dates.