I've had three babies over the last 4.5 years. (The other week I dumped the pill so I didn't screw up THAT again and am on the depo shot until I graduate in the spring. The last thing I want to tell my boss is that I've failed at birth control again and I'm having baby #4 while in grad school)
Consequently: I have jeans and pants of all ranges of sizes (including those stylish elastic band top ones, my favorite of those are my Old Navy ones that striped the elastic band instead of "disguising" it blue to "match" the blue jean pants, yeah that doesn't fool anyone idiots!). I don't shop at grossly expensive places, I usually shop at places like JCPennys, Sears etc. But sizes are like ALL OVER THE PLACE.
I'm ridiculously pleased I just got back into my favorite jeans, name brand Ana from JCPennys. However, I also just finally lost enough weight to get back into a couple of pairs of shorts from my Junior year of undergrad, Size 14. (how does that make sense?) I can also squeeze into a size 8 Levis I picked up from Sears before I got pregnant with Baby #3. So right now I'm wearing pants sizes ranging between 8-14.
For 15-20 bucks, I suggest you go comb the racks of a couple different stores and find a pair that you feel good in. (I wouldn't spend 30-40 dollars on a pair you might never wear again though) Feeling good in your pants is a HUGE confidence boost to me. And feeling good about myself is almost "half the battle" for weightloss for me
I usually notice I lose the slacks when I'm dropping weight, before the jeans though, but I think its because they dont shrink or get tighter every time I wash them like my jeans. I have to wear my Ana's for about 10 min before they stretch back out after a good wash LOL!