You do not need to show anything at the beginning. Just open Thai company Limited with 2,000,000 capital (you do not need to show these money either).
Get 4 employees and go ahead. You can count to spend approximately: 35k for incorporation, bank account and SSO about 10k, Work Permit 15-25k, Visa 30-45k. Easy... but for next extension you have to show that company has some activities.