I'm looking to get a sleeping bag for the occaisional camping I do. However there seems to be a wide array of choices and I'm not sure what factors/features are best for what I intend to do. What I'm looking for is a good quality bag, fairly versatile that will be good down to about 20-30 degrees and that can unzip to be a blanket. I plan on using it spring-fall maybe four to six times a year, but there is the slight possibility that I might backpack with it as well. If I can I'd like to find such a thing for around 60 to 70 dollars. What are some good options?