Comparing Jomtien immigration with Bangkok immigration is of no value. I used the emailed statement earlier this year and it was readily accepted without a stamp. Jomtien doesn't have a good reputation with expats
Ok. It didn't work for me, so the OP can take a chance on what you say. It's their choice. It's just as easy for me to order 12 months statement from my local branch, which takes five days and 100 baht and I know 100% it will be accepted. I wouldn't take the chance just to save 100baht - but as I always say, each to their own
You're better off building up your nest egg in your home country earning a slightly better interest rate (not much admittedly but everything adds up) and when you're ready for the visa transfer the 800k lump sum in one hit.