If modest accommodations are your thing I'd look at
Happy Holiday Homes in the Belnem neighborhood south of the airport. We stayed there for a few weeks in 2010 and had a great time. HHH offers clean, fully furnished, and modestly priced accommodations set a couple of blocks back from the ocean. You should be able to get a 3 bedroom apartment for ~$168/night, including taxes and service charges. That works out to $56/person for private bedrooms and shared living and cooking space. Energy is expensive on Bonaire, so they charge an additional $10/day per bedroom if you use the A/C. On our trip we were content to just run the ceiling fans in the living areas and bedroom. The windows and doors are screened so you can take advantage of the trade winds for additional cooling.
You didn't mention details about your group. If 2 twin beds in one bedroom suffices for part of your group, you can save some money by renting a 2 bedroom apartment. Most of the bedrooms are equipped with "European King" beds... I.e. a pair of twin beds pushed together. Tell Louise, the owner, what you're looking for and she'll suggest some options.
Buddy Dive's Belmar Apartments dive shop is a few doors away, so that would be the closest location to get tanks. You can also take advantage of the other Buddy Dive locations at Buddy Dive Caribbean Club for no additional charge.
Louise can also provide additional suggestions for diving and car rental etc. The HHH website is pretty basic too, but you can get an idea of the vibe by checking out
HHH photos and reviews on TripAdvisor. Be aware that Louise also manages a separate nearby oceanfront property through HHH too. Any HHH photos on the web showing oceanfront views are of this other property. PM me if you've got any specific questions.