There are currently over 4000 expats living in Hua Hin. They are attracted to Hua Hin among other things by relalively low living costs. Of course your living cost are dependent on you live style.
The biggest living expense in Hua Hin is accommodation. If you intend to stay longterm you should consider buying a condo. As for renting, expect to pay between 30,000 and 70,000 baht for a 2-bedroom furnished apartment. This would include access to a swimming pool and exercise room, most likely also a sauna.
As for home living expenses, aircondioning takes a lot of electricity. Using it around the clock (dayttime in the living room, nighttime in the bedroom) will set you back about 5,000 baht. UBC cable TV costs 1,500 baht for the standard package. ADSL broadband is between 1000-1500 baht per month.
There are really a lot of restaurants in Hua Hin, both cheap establishments and fancy ones. It is possible to have a decent two-course meal, excluding drinks, for between 150 and 250 baht. But there are restaurants which will that is anything to go by, the seafood buffet at the Sheraton Grande Sukhumvit will set you back set you back by 1000 baht.
We actually suggest you eat a lot of the time at home. Eating at home has the advantage that you basically know what you are eating, and should often be much healthier than foods from restaurants, where you do not have control over the ingredients, and especially over the cooking oil used.
There is no need to own a private car in Hua Hin. Taxis and Tuk Tuks are cheap and cost 100Baht for a trip within Hua Hin. Petrol cost 25 - 30Baht per litre.
Labor costs in Thailand are low. Thai government has a policy of keeping wages low. It is quite cheap to hire people to do repair, DIY jobs, maids or gardeners.