If you are on the fence about buying cycling shoes for your spinning class, get off that fence and buy them.  You don't need to shell out $300 on pro shoes, these shoes are fantastic.  You can ride faster and transition from sitting to standing without worrying about the straps becoming loose or your foot flying off the pedal.  You can also pull up on the pedal, as well as push down, which works  more muscles.  If you tried that with sneakers and foot straps, the straps would snap.
I'm a woman and these are guy's shoes, but these are sleek, they're stylish, and they've got an aggressive look to them that the women's shoes lack.  They also have free 2 day shipping with my student Amazon account. They're also great because they are mountain bike shoes, and when you get off the bike, the tread is deep enough that you're not walking right on the metal clips (which you must buy separately) like you would be on road shoes.  I wouldn't suggest taking a long hike in them because what makes them effective for cycling is that they're rigid, and so they're kind of awkward to walk very far in.  But if you wanted to go walking in them, you could.
If you're going to buy online, I suggest only buying the shoes and then heading to a bike shop to purchase the clips and have them attached, unless you really know what you're doing.  The guy at the bike shop has to do some measuring and he knows exactly the sort of clip you need.  I also recommend getting half a size or so larger than you normally would.  I'm a size 7.5 in women's so normally I would have gotten a size 39.5 euro, but having tried a few pairs of shoes on at the shop, I found that cycling shoes run a tad small.  So when I found the style I wanted online, I went for the size 40.