Networking computers

Hello,
I have a computer hooked up with a DSL modem/wireless dual band N router ( NetGear ) I tried to set up a wireless connection to another desk top computer about 50 feet away using a ( NetGear ) dual band N, USB plug-in adapter and the connection is not good - it's less than 50/50 that I can make the connection when I try and I thought I could just run an ethernet cable from the Router to the new computer, But I think a 50 foot cable is going to cost a mint. I do already own some 50 to 100 foot networking cables- but they are standard phone connection wire and jacks. They were used for networking multiple computers together that run a proprietary software program in my business on Linux. Anyway, is it possible to use those cables to connect from the original computer to the new one and access internet without having to get the long ethernet cable ? I Thought maybe setting up a local network, but I don't know how..................