I have bought stuff on Craigslist and eBay. The only problem is that you need to know what you are looking at and what it is worth, which a beginner may not know. I've seen sleeping bags on eBay sell for more than retail, which is ridiculous.

Check through the sponsors' ads-they may have some packs on sale. Also check the REI outlet and Sierra Trading Post for deals. You don't need the latest and greatest, you just need something that is well-made and comfortable. Price is not necessarily an indicator of either one.