I understand taking out cash in Thailand is costly since exchange rates are not that great and there are hefty fees on withdrawals.
If I am able to more less estimate what I will spend for the duration of the trip (then add a few thousand more) should I simply take it as cash (which solves the high fee withdrawal problem) or is there a 'better' way, like a magical 0 fee card, or some alternative?
Should I bring as much cash as I can when traveling to Thailand?
No, you are allowed upto USD20,000 or its equivalent out or into Thailand.
Source: Royal Thai Embassy
BRINGING CURRENCY IN OR OUT OF THAILAND
Any person who brings or takes an aggregate amount of foreign currency exceeding USD20,000 or its equivalent out of or into Thailand shall declare such amount of foreign currency to a Customs Officer.
Failure to declare upon bringing currency that exceeds the amount restricted by law or its equivalent out of or into Thailand or making any false declaration to a Customs Officer is a criminal offence.
Does it make sense to bring as much cash (up to 20k USD) as possible when going to Thailand?
No honestly you can carry upto 20k usd in Thailand , it is not a good idea to carry that much cash with you while traveling. It's often a good idea to get some foreign currency before you leave home so that you have cash on hand to handle your immediate expenses -- like buying a meal at the airport or taking a cab to your hotel.
The best options are carrying credit cards/debit cards, travelers checks and very little amount of cash while you travel.
It depends entirely on the reason why you want to take cash:
If you have a bank account that charges low fees on international ATM withdrawals and foreign currency payments, you're better off just using your card. Whatever exchange rate you will get for your USD probably won't be better than the rate at the ATM.
If your bank doesn't have a low-fee option, I suggest opening a virtual account with Revolut (disclaimer: it's a referral link which gives a small bonus for sign-ups). It's a zero-fee bank card that is available to all European residents without visiting a physical office. You order it through an app, receive it in the mail, and then top it up with your regular card (in EUR/GBP). Revolut is also great because it charges the inter-bank rate for all foreign currency transaction and is usually on-par with Transferwise.
If you prefer cash just for the sake of it, then yes, bring as much as you need.
Beyond whatever option you choose I recommend getting at least 200$ in emergency cash. You never know when you might need it.
