I like the Medela CSR bags I've used, but I haven't used any others for comparison. I don't think the price varies much, at least I don't remember seeing any huge discrepancies between stores.
I used the bags for milk I was going to freeze; for milk I was feeding within the next couple of days, I pumped into bottles.
Come visit the NEW QuirkyBaby website -- earn QB Bucks rewards points for purchases, reviews, referrals, and more! Free US shipping on great brands of baby slings and carriers and FREE BabyLegs or babywearing mirror on orders of $100+. Take the QB Quiz for personalized advice!