Hi! This is only my second runDisney weekend, so I'm no expert, but I know I had a LOT of questions before my first and found the disboards to be very helpful. I don't know anything about air bnb, but I just wanted to give you some things to consider/compare when figuring out where to stay.
The first thing that I thought about after reading your post was transportation. Will you be renting a car? Taking cabs/uber/lyft/etc? Keep transportation costs in mind when deciding where to stay. We stayed at Pop Century last time for Princess weekend. Originally we were booked to stay off-site, but then changed our mind after considering the price of the rental car. We lucked out and were able to book our room on New Years Day with a promotional discount. It was the only value resort still available for our dates. While it may not have been the most cost effective choice, it was ideal for us because:
A) We like staying in Disney.
B) Transportation to and from the airport is included.
C) Being new to runDisney, it gave me piece of mind knowing transportation to and from the expo and all of the runs would be provided. I was most concerned about driving to and from each run at 3 in the morning, not knowing what traffic would be like, and not really knowing the area.
A lot of people stay off-site for Disney trips, and a lot of people drive to the runs (which does sound preferable, I would've liked to have had the option to sit in a car while waiting to enter the corrals before the races started!). I'm sure you'll get better advice here. I would recommend putting all of this into consideration, and price out all of your options. If you have the money to make reservations/deposits in the meantime (as long as they are refundable) I would try to make one where you think you are most likely to stay sooner than later. I know Princess weekend is very popular, so I'm not sure how quickly places will fill up.
A small piece of advice - we've started using is paying for our trips with Disney gift cards. If you have a local Target nearby and have a Target debit or credit card, you can save 5% on gift cards. Not a huge savings, but every little bit helps! We see it as saving 5% on purchases we would already be making anyway (food, souvenirs, your room, etc). If we are planning a trip, I'll pick up a card or two on each Target run, combine then on the Disney gift card website, and put them away for our next trip.