Right, you can get a wireless USB link thing that just replaces the USB cable – but that looks fairly dodgy to me. A lot of printers have the ability add a bluetooth dongle for wireless printing – it’s not as good as having a wifi printer server, but it is cheaper and it works. Also means you can print from your phone too, and anything else that’s bluetooth.
As for hard drives – you’d be effectively having network storage. That is, your hard drive would be a stand-alone thing that sits on the network alongside your other computers. That’s not particularly cheap (google wireless NAS (network aware storage)) but you can also get some wireless routers that you can plug your hard drive into and it does the same thing. Your current router might have that ability already.