I found this interesting site that could be useful to a lot of us in our search for components across numerous suppliers. This site lets you upload a list of parts (xls, txt, csv, sch) and then searches the availability across multiple suppliers. It will then optimize your order based on prices. Unfortunately, it doesn't seem to take into account shipping. But I still think that for big orders it could be really useful. They have some example BOMs you can use to try it out. One of their examples is even a linestage from twisted pear audio.
I remember spending lots of time trying to figure this out manually for some projects. This would have saved me a lot of time and frustration. Enjoy! :)