>>2468>where do you get your salvaged tech, OP?
Seconded, I'd love to have 40 hdd's to fool around with.
Unless you're actually trying to salvage the chips, I think that pretty much every chip that you can pull off either has silver-plated, silver, gold-plated, or gold contacts. From what I've read, 1000kg of misc. circuit boards end up having about 0.5kg of impure gold in them, so you might actually be able to make some money off of that. Whether or not it's worth your time is for you to decide. If you want to actually recover the more pure metals, you'll need to invest in chemicals to do so (probably not worth it for 40 hdds), or you could send the unrefined pins to a company which specializes in this sort of thing.
Very rough estimate- 1kg of drives might get you something like $20 if sold to a specialty shop. This is from 10 minutes of googling, so take that as you will.