With sleeping bags you can pretty much get as crazy as you want to get and spend as much as you want to spend. Sleeping bags can range from $75.00 to $375.00 and there's probably ones you can get for even less and ones you can get for more.
The two big things about sleeping bags that you need to think about are warmth and weight. If you're going to be camping in the summer then you really don't need to worry too much about warmth. If you're going to be camping in the winter or really in cold weather then you're going to need to look really closely at the temperature ratings on the sleeping bags. For the most part a spring and summer bag or a fall and summer bag is going to suit most campers.
Filling is what's making your bag either warm or heavy, or heavy and warm, or not too warm and very light. So if it's a down bag, down is great because it's really light and really warm. But, if you have a down comforter you know that down tends to bunch up all over the place. So down is not as reliable and it usually doesn't last as long as a synthetic bag. Synthetic bags are warm but they're heavier. They're also more reliable. They're not going to bunch up and they're going to probably last a little bit longer. The other thing is that if down gets wet it's pretty much useless. So down is a little more temperamental. Again, it really just depends on what you're looking for and what kind of camping trips you think you'll be going on.
Roughly speaking, a three pound bag is what you're looking for. Anything more than that is going to start to feel like too much to carry on longer trips. And when I say longer trips I mean more than a two mile hike into your campsite. Five pound sleeping bag is definitely too heavy.
Sleeping bags also are shaped differently. So there's rectangle bags and then there's mummy bags. And that just means that the legs are sort of tapered on the mummy bag. Mummy bags are warmer. They're a little more constricting. They're also usually lighter. So again, you just want to weigh the pros and cons, what's important to you and the kind of trip you're going on.
When I first started camping, and probably for the first two years I camped, I used a crappy old comforter. I would just fold it in half length wise, fold it in half again, roll it up super tightly like sushi, wrap the whole thing in rope and that was my sleeping bag. I tied it to the outside of my backpack. You can do that too. You don't need to spend a lot of money. If you're going on a really long trip to somewhere really cool, that's when you're going to want to invest in a really great sleeping bag. Otherwise, you can get by with a lot less.