All but some of the cheapest resorts will pick you up in town and send you back for free, but all charge for going out to the Phetkasem Hwy.
The beach at Bang Saphan Yai is 6km south of the town via Rte 3374 – you can't miss the turn-off as there's a mass of resort signs. Ban Krut is 1km to the beach, though most of the accommodation is spread out far from the junction. Moto-taxis from Bang Saphan Yai to the beach cost 100B, from Ban Krut it's 20B to 30B.
In Ban Krut, Siripong Guesthouse and Bankrut Tour & Travel rent motorcycles for 200B per day, as do several other nearby shops around the junction. Several shops at Bang Saphan Yai's beach also hire motorcycles for 250B to 350B. Another option is to hire them in town at Tae's Restaurant, just down from the train station for 200B to 250B, though this is a very casual operation and they're often not available.