if you do it yourself,you have to take a letter from immigration saying you are of good character. That's why you need a thai person to vouch for you. They charge 500 bhat.You take it back to the bank & it's 300 bhat for the bank card. Every year they charge 300 bhat to keep the bank account open. Tbh i would pay an agent if i had to do it again. It's a lot of hassle.
If your healthy then why not wait a few years before you get insurance. Ifyou ride a motorbike then i would simply get accident insurance off your bank,small money.