I am a frequent user of BrickLink, and often after creating a Wanted list, I would find no one vendor with everything I wanted in stock. The resulting manual search for the least expensive mix of vendors to purchase from was time-consuming. Therefore, I wrote an automated tool to do this search for me which I'd be happy to share.
For a given Wanted list, my program downloads BrickLink pricing info for all desired pieces and does a search over all possible vendors to find the combination that fills the order at the least cost. It can also filter on New vs Used parts, specific or undefined color, US vs international sellers, and split partial quantities over multiple vendors if desired totals can be met.
My solution is a package of Matlab scripts which I can share with anyone who asks; just send me a message. The tool does require Matlab, but I'm probably not the only Matlab-using engineer in this demographic, and I'd welcome any effort to make this into a stand-alone executable. The example for parsing a Brick Link Price Guide page might be helpful to programmers on its own, and I'd also be interested in hearing about any other solutions that solve the same problem.