I have used a Western Mountaineering Badger MF as my primary bag for the past 7 years. It isn't cheap, but I know when it is pushing the 15 degree mark, it is truly a 15 degree bag. I can't say that about many of my other sleeping bags which claim even a 20 degree rating.
http://www.westernmountaineering.co...eping Bags&cat=Microfiber Series&ContentId=34
I have since added WM bags for summer and winter use, plus a rectangular Ponderosa for shoulder season camping.
Davy's first post is spot on.
When I worked for Kirkham's, I had people wanting to buy sleeping bags, but they wanted a down bag with a price tag of $200 or less. I stressed to them the importance of a comfortable night's sleep and encouraged them to save their pennies and buy the best bag we sold (WM bags). I had people come in and thank me after the fact.
If you are a weekend warrior, KOA camper, or you only camp in the summer, a cheaper alternative is just fine. If you venture where you must trust your gear with your wife's happiness (
) get a quality sleeping bag and a quality pad to match.