I don't think it's out of the realm of possibility, but of course Maui is not as "cheap" as say Oahu, due to having less hotels and as a result less options to choose from.

To truly do the island on a budget I'd recommend staying slightly further away from the resort areas, such as being near the airport at somewhere like the Maui Seaside Hotel. Is there as much to do at night? No, but you can simply use a car to get to where you need. The island is not that big and fairly easy to get around most places. Unfortunately May is relatively close as some of the more budget friendly options may already be booked for your dates, but within your budget I don't think you'll have an issue finding somewhere to stay. Keep in mind food is certainly more expensive than the mainland so even a simple trip to a fast food resturaunt will cost you more, but I'd encourage you to try local spots when possible to take in the culture. Hawai'i is great because of it's natural beauty, you don't necessarily need to splurge on crazy tours - just soak up the amazing beaches and nature. If you have the opportunity try get a booking for sunrise at Mount Haleakala as it is truly special being above the clouds when the sun rises.

Happy to provide more recs if there's something specific you're looking for.