I'm finding out that Craigslist and other places to get used phones aren't so bad...the only real big problems are:
-possibly getting a stolen/broken/etc. phone that has a bad ESN.
Ways to avoid these two are to meet at a public spot like the Sprint store. Once there, you can ask Sprint employees if the phone has a bad ESN or not.
Phones sold used are typically cheaper and when seen with Sprint's pretty good insurance policy...you can get a sorta brand new phone if anything happens for real cheap.
I bought my Samsung Moment on Craigslist for $150 when it was still $400 brand new from Sprint and when I broke it, they replaced it for $100. Do the math and I still paid less than MSRP. Refurbished phones are kinda wack sometimes though