Vendor prices now vary more than they used to from vendor to vendor. I've put up a post on my blog explaining how the new system appears to work: http://mathemaglitch.blogspot.ca/2012/04/vendor-prices.html
For those who don't like long-winded explanations, though, Tool Vendors are still the place to sell, but only buy at 75% right now, as opposed to the 80% they used to.