I've been staying one week in Chabakaew Guesthouse. It's a small wooden house with 4 rooms located on the sea front. Two of the rooms have a balcony with a wonderful view on the sea for 500 bahts. The rooms are quite basic, but there is everything you need including private bathrooms
You can also rent bikes and motorbikes at cheap price and have free wifi.
Most of all, the owners were very friendly and helpful. They told me everything i had to know about Prachuap and the surroundings. they also invited me to have dinner and a few drinks, wich they apparently do often with customers.