There are Spas by the dozen, and as Kuta is the most competitive place in Bali, prices are the lowest. Shop around and ask for package discounts. Take a look at the place first and do not allow yourself be talked into something by touts.
A well known spa is Villa de Daun on Jalan Legian. Reborn and Cozy are two excellent spas on the outskirts of Kuta, on Sunset Road just before the roundabout. The price is around IDR 120,000 for two hours, but some spas have "happy hour" specials. Carla Spa, located on Poppies has a very good full body oil massage for not too much money, ask for Alfa. Opposite side of Artawan, same side as "The Steps", a bit further towards JaLan Legian IDR 50,000 for an hour.
Beware of the women offering massages on the beach. They are seasoned at ripping off tourists: be sure you have agreed to a price and a duration, or you will find yourself with only a ten minutes massage. Meanwhile, some professional masseurs, with license numbers on their conical hats, also offer massages on the beach and worth to try.