ALM or KLM used to do the flights, but they went under. As did an airline called something like "Air Aruba".
For the most part, believe it or not, You don't have many options for going between the two islands. Aruba Fly and Dive will do a charter (private) and I don't know what that costs.
Are you planning on staying in Aruba for some time or just wanting to use it as a connection point? If you are wanting to try to use it as a connection point, I'd reconsider and try a more direct route to Bonaire. The "connection" airlines there aren't just dependble since there isn't a big demand on tourist travel between those islands. That and the time required to go through a seperate check in, seperate customs/imigration, etc. It's just not worth the extra time and expense.