I am not a huge fan of Old Navy jeans. They tend to stretch very quickly once you have them on!
Here's my surprise discovery of the year re: jeans... Target! I'm still dropping the last 10 lbs of baby weight, but wanted a cheap (but nice looking) pair to get me through and found great jeans at Target.
Kohls is pretty pricey for Levis. My husband has to get his work jeans at Kohls b/c of their contractual agreement and I was SHOCKED by what they charge for a pair of Levis. The hubs is an engineer and their company buys them jeans to wear "on-site" so they don't ruin their khakis... AND they launder them! Yay, but still pretty pricey for "throw away" jeans.
Also check Marshalls and TJ Maxx.