1000' box of cat5 can be had for under $100, well under if you know where to look. That should get you anywhere you need to go :P

Yes you can. You can bridge the wireless and wired connection. If you open up your network connections, select both the wired and wireless then right click on one of them and choose "Bridge".

I'd rather use 3 feet if I can connect the LAN of the computer into the "connection to modem" of the router and avoid chasing the wire halfway across the house.

You will not want to use the internet port on the router though! It should have some standard ports as well right? You need to go into the settings and turn off DHCP in the router, then connect it to the LAN on the desktop through one of the standard ports. You also need to make sure it is on the same network as your main router, but the address isn't conflicting with the main router.

I can give you a quick lesson in IP addressing if need be.

I would think it'd be easier to enable internet connection sharing on the pc. That way the ethernet port on the pc will output the internet to the router.

Confused now, I went to network connections and established a bridge and a bridge icon came up. won't that output the internet connection to the LAN port on my computer?

which windows are you using?

It'll essentially allow traffic to pass through between both ports

I would recommend Internet Connection Sharing... highly.

Yes. If it'* running Windows, just bridge the wired and wireless interfaces (right-click them and choose Bridge). It would require that computer to be on (and not in sleep mode) 24/7 though; easier than running cable, but your power bill may not be happy.