Hawaii on a budget means the Wailuku hostel, county campgrounds and accepting the rental car.
Banana Bungalow, Wailuku
The island's long-standing backpacker house, in old Wailuku rather than the resort strips, with dorms and free day tours that solve the no-car problem.
What a day costs
About $85–150 a day: hostel bunk or campsite, $25–35 on food from Foodland or the Kahului big boxes, plus a share of the car.
Coast and summit camping
Camp Olowalu and the county waysides take tents by permit; Hosmer Grove inside Haleakalā is free with park entry at 6,800 feet, and genuinely cold at night.
The bus and the car
County buses run a couple of dollars a ride between Kahului, Wailuku, Kihei and Lahaina, but reach neither Hana nor the Haleakalā summit. Most travellers split a rental.
Free by day
Every beach in Hawaii is public. Ho'okipa's lookout has turtles hauled out most afternoons and windsurfers offshore; the Kihei beach parks cost nothing but sunscreen.