See, wouldn't a budget-fi subforum be great now?
OK, since you're worried about sound leakage, I'd recommend: Sennheiser HD201 + Fiio amp.
The HD201s are great for the price (~$30) and they improve a lot when paired with the Fiios (~$10). Plus, despite the pleather, they're pretty comfy and I never got hot/sweaty ears. So, that's $40.
Now, if you're going to consider anything more than $50, I'd say the Denon D1001s if Amazon.com still has them for $70+. They can go unamped. The verdict on the 1001+Fiio combo is ambivalent, but I don't think the Fiios do anything good to them. Unless you really like your bass.
If you go for the HD201+Fiio combo and can find a pair of KSC75s for cheap, you should def. get those too. Heck, even if you get them from street price, that doesn't put you much above $50...for TWO headphones and an amp. Sweet.