You forgot the most important source of all... Ebay. I just love the Chinese sellers of electronic components on ebay, have not had any bad experiences. Takes some time to get here but you get free shipping from most.
You should visit those sites as they differ quite a bit in layout as well as what they offer. Some are better for some things, some are easier to nav, some charge for shipping and some take a chunk of forever on delivery, etc. How can you can know how to present them if you don't check them out?