@Dean ******
As much as you want, but you’ll have to declare it when it’s more than 20k usd.
There’s no specific “border taxation” on it. Note that, under current tax laws, money brought in which originates from taxable income will become subject to income tax in the fiscal year it’s brought in.
If you come as a tourist and remain under 180 days of staying in Thailand while bringing in money, there’s zero charge.