Can anyone expand on this? Perhaps some alternative to ebay that sells by the kilo
local flea-markets for example, thrift stores, craigs list, other auctioning sites...
on craigs list and newspaper classifieds you could even ask. some people keep their old lego, waiting for an opportunity to give/sell it to someone who deserves/needs it instead of selling it to someone looking to make a profit.
it takes some searching, patience and good luck.