A really good starting point would be to do a quick search, as there are lots of prior threads with recommendations. Even if you don't want to confine yourself to advice from here (and you really shouldn't) they'll give you a good starting point. Prices range from around $40-50 to in excess of $400 but obviously ones in the upper range aren't good starter guns. You'll find my usual beginner recommendation in a number of the prior threads, an Aztek, along with all the reasons I think they're the ideal choice for anyone who has never airbrushed before.
You'll also need to think about air supply and for that the best option is usually a compressor; to prepare you, unfortunately these will often run you more than the AB. Again, lots of threads on compressors of all kinds and across a very wide price range. The worst choice by far for air is cans, so I'd strongly recommend not even considering them - easy to empty one just messing about with a single colour and then blowing through during the cleaning stage.
Einion