For a hundred bucks, you won't get much. lightweight bags are usually filled with goose down. If you want a usable bag, you'll want one that has a gortex shell, otherwise plan on being wet and cold. Holofil bags (synthetic) are warm even when wet, but they weight more than a down bag. For what you are describing, you can find a 20-25 degree holofill bag. It may get you by, providing you have a good tent. Personally, I won't go out without a 0 degree bag, just in case. I've done the same experimenting and spent alot of money on bags that I just have around the house or in the back of my Jeep as Throw blankets or beach blankets. Do yourself a favor and look into spending at leat 200 on a bag. It'll save you in the long run. Look around local shops, browse REI and EMS, but before you buy, see if you can find it at [url=www.campmor.com]Campmor[/url]. I've found equipment at half the price at this site.