The best advice I can give is go to a shop and try various makes on for size - and not for a second or two, leave them on for a couple of minutes, you'll soon get an idea of how they are. For example, DCs have something of a reputation for clamping your head, Sennheissers tended to feel as if they were perched on top of my head, various Bose and Lightspeed models fitted nicely, I eventually settled on the Zulu2 because of price and the fact that Lightspeed's customer service is infinitely better than that of Bose.
Once you know what fits comfortably, you can then determine how much you want to spend. I would always tend towards active headsets but if your budget only stretches to passive, just make sure they sit right, nothing is worse than being in the plane trying to learn with an uncomfortable headset on, giving you a headache.
Finally, if you think an active headset is too expensive, just divide the number of hours you expect to fly with that headset over the price - mine worked out around £1 an hour. Well worth it. But before you decide go somewhere to test and then decide based on price.