Hey MC,
Oahu is pretty expensive and the only place to kite where your girl may be happy is in beautiful Kailua Bay which is on the other side of the Island to Waikiki where all the hotels are. It's a great place to snorkel, kayak and so on but if your girl likes to rattle the plastic, she'll need to be in Waikiki which is unkiteable unless they get Kona winds which is in the off season ... er, like now!
Accomodation is best sorted by rocking down to the beach and asking around with the local kiters there. Always someone looking for a roomy or looking to let a room to ease rent. Kailua and Lanikai are setup for the big money tourists looking to get away from it all with rooms and sometimes freestanding B and B type accom on the beach can cost as much as $400 USD per night! I rented a room for $600 USD a month with shared facilites but very nice pad and cool roomys.
A bike or cheap rusty car is easy to afford if you get advise from the locals.
For a stay of any length you will need to be either a rich kiter or you'll need to work. You could stay about a month before you'll go broke if you dont work with a few grand.
Aloha and Happy New Year!