Accessing your money is generally not a problem these days in Hua Hin. All the major Thai banks are represented here and there are plenty of exchange booths and ATMs everywhere.
Your biggest concern will be how to keep your money safe. Thailand has a bad reputation worldwide for credit and debit card fraud and you should always be aware of this. Never let your card out of your sight. Theft in Hua Hin is more likely to be as a result of trickery and deception, rather than violence, but it's always a good idea to keep the amount of cash you carry down to a minimum.
Most travellers will come with a choice of ways to get at their money, with travellers cheques and credit/debit cards being the most popular. You'll always be able to exchange travellers cheques at exchange booths 365 days a year, but most don't open until 10am and close around 8pm.
It's also a wise move to inform your bank back home that you are visiting Thailand and Hua Hin. They are increasingly taking note of where ATMs are being used and may well block your card if they see it being used here. A telephone call back to them will normally get the problem resolved, but forewarned is forearmed. Your bank will also generally take a commission every time you use your card, so check with them before you go - it will make a difference.
The Thai Baht has strengthened enormously over the past two years and the indications are that it will continue to do so in the foreseeable future. The recently introduced practice of Thai banks charging a 150 THB fee for all foreign debit/credit card withdrawals from ATMs also does nothing to help the value of your foreign currency. One branch that is not charging this fee (at time of writing - January 2011) is AEON on the third floor of Market Village.