yea it's very easy to get off the pier at haad rin, once you land just walk past all the taxi drivers, if you continue straight down that road you'll walk by a whole bunch of resturants and shops, you'll come to a place where the road goes to the left or into a guesthouse, go left to follow the main raod and then continue on down past the 711, you'll hit the beach!!
There are TONS of guesthouses around, but the prices have started going up already, some of the cheaper ones we've found: (we've been hunting for a few days now checking out prices for ourselves)
SK Home, it's directly above the 711 in town, 340 a night for a fan room with private bathroom, the down side with this place is that it's boiling hot pretty much 24 hours a day (got in a 3am last night and had a hard time falling asleep with that), but if you don't mind the heat it's very central and clean! you can't use your own padlock on the door though and the staff keep the key and clean up the room for you every two days.
and Yoghurt home 3, it's directly behind Tommy Resort, we're paying 400 a night for a huge room with private bath, fan, and a nice balcony. I'm not sure if there are any fan rooms left here, I'm pretty sure there are some aircon ones avaliable fofr 600 baht. I think if you arrive tomorrow I think the rooms go up 100 baht but I can ask.
we found some others that are between 400 and 600 but some of these places are jacking the price up by 1000 baht just for the week of full moon.
What time is your plane landing at Saumi? The last ferry from Samui to haadrin pier leaves at 6:30. You can get a deal at the airport for 300 baht, it includes taxi and the boat, it's a really good deal as the ferry is 200 and when we were on samui the taxi alone was 300.
When your walking through town keep your eyes out for alittle booklet called Ko Phangan Info, it's really helpful and lists quite a few of the guesthouses, with a good map of all the guesthouses in haad rin. Mostly the Bungalows are going to be priced way to high for the time of year because of full moon, the dorm style or guesthouse style are the most affordable!
Good luck!! let me know how it works out.