commuter/ travel bike
For that price, you are going to be hard pressed to get even a good used F650. probably more likely an older Funduro (90's) model, but you might pick up a good used early 2000's injected bike. Great commuter bike. Will it work for two up traveling? Yes, but there are limitations and comfort issues. It is what you make of it. If that is your budget, you can find a way to make it work....
I'd consider an older Honda Transalp or such, might fit the price range and also be a bit better 2 up.