Yesterday I picked up 17 kg of Lego for about £320, mostly space related, so it should be a good haul. It was in the local classifieds, so I could meet the seller, and take a look it before deciding to buy. This is important, I looked at another batch earlier and there were not that many useful parts in that one, it also saves on shipping.
I'm about 20% of the way through sorting through it, and have a lot of parts for the Falcon. There is a mixture of old and new greys, but all the parts are in very good condition. I've got a lot of the plates and the special bricks, lots of engine grills, roof bricks and other parts. Only 4 levers and one telephone receiver though...
If you plan to do this you will need to invest a lot of time sorting through it all. Checking parts to see if they are in the inventory takes most of the time, but gets quicker as you learn what is what. It's also a little disheartening to find a piece and think "Do I need one of these?", then find out you need 94 of them. Its more fun that putting in an order though, I'd recommend it if you have the time. If you know your stuff, which I don't, you may will come across some rare parts to trade.
Not sure if I will save any money this way, or if I will sell the unneeded parts or keep them for the kids. Hopefully it will get me started with many of the bits.
I'll let you know how this worked out in $ per part when I'm done.