I love to get my books used if possible. I don't mind if the cover is scratched or the spine is creased. As long as it's legible and doesn't have an odor.
I sometimes go to a used book store in town, or a church will have a big used book sale, or I look on Amazon.
I have a 2 year old and I'm 36 weeks pregnant so I wanted to search online rather than go in a store.
I found a used book site, thriftbooks.com, that had the best price and shipping options. The used books I was looking at on Amazon, were only a few dollars cheaper than buying new. On thriftbooks.com, it was only $3! You pay $0.99 for shipping under $10, or shipping is free over a $10 order. Shipping was fast as well. I ordered my books on the 30th and got them today. They also have 15% off now too.
Just wanted to spread the word and save you some money! Hopefully you have the same experience I did.