handy find at autojumble . various size roller bearings all hardened and ground for 2 quid .they make excelent cheap paralells for setting jobs up on the milling machine
As above use the whole bearing casings. Shelf next to the lathe with all sorts of old bearing oddments and stuff to use as precision spacers or test pieces. A large roller ball bearing with a flat ground into one side facing the moving jaw is great for gripping uneven stuff in the mill vice properly also as it pushes the workpiece into the fixed jaw and lets it flex to ensure its touching all the jaw and not at one end.
Older dot matrix printers + flatbed scanners used to be a good source of cheap precision ground rod in longer lengths, but theyre thin on the ground now.
Use halfshafts here too, I have a mate who saves them for me & I'm always raiding his garage scrap pile when I nip round there for something. Nick the rollers out the bearings, use the shaft itself for high quality bar stock, even have repurposed the spline and sockets for other jobs now and again (the clutch on my dragbike has a renault master van spline on the friction plates and the matching male spline on the gearbox input shaft, same price for a new length of matching splined bushing stock in that approx size about £600!)
I hope this thread snowballs into a cheapskate method of tooling use, always interested in what other skiprats come up with.