Ok, so you more or less have all the info to answer this question. Go to your statement and see how many points you earn on average a month.
On Amex you can get most gift cards at about 100 MR pts per dollar - haven't checked Airbnb specifically but hopefully it's the same conversion. You mention having a bank, so you probably don't have Amex, but you can calculate redemption values pretty easily on your rewards portal.
