I'm in scounging mode also. Frankly it is the only way I'm likely to get the majority of this machine.
As to motors do look for pen plotters and similar devices. Old band printers might do the trick also, you are just as likely to find worn out components in the band printers though.
I would have to say the price that you are mentioning for the aluminum might be OK. I don't know as I was lucky enough to scrounge a little bit for some machine ideas I have.
Unfortunately I'm in the Rochester NY area so I cna't help out there.
I'm thinking though that you have a huge opportunity if you are near the Boeing facilities as I though at one time they had a public sales area for used stuff. Of course that is $$$$$ but you neve know what you might find for cheap. At one time they also where associated with DoveBid.
In the city itself you might find one or two electornics "junk" sales organizations. That is places that handle old stock and discontinued stuff. Still a $$$$$ issue but often very good bargains to be found.
The only other option is to get access to industrial junk. That may or may not be a problem.