Thailand is one of Southeast Asia's best value destinations. Budget travelers can live well on $25-40/day: a guesthouse room runs $8-20, a pad thai from a street stall is $1-2, and local buses/tuk-tuks are cheap. The famous Thai massage at $8/hour is a budget luxury.
Mid-range ($70-120/day) unlocks air-conditioned hotels, sit-down restaurants, island ferries, and day tours. Island-hopping can add up — boats and ferries between islands cost $5-30 per leg. Bargain at markets but not in small shops with fixed prices.