I did something similar at the ranch. Early on, I was getting DSL from my tenant who had paid to put it in. Later I provided DSL to a subsequent tenant from my own subscription. The rental cabin is some 75 ft from my wireless transmitter located in the house, so I bought an 'access point' and configured it as a repeater. I put it in the sunporch where the cabin could 'see' it without obstacles. This repeater worked well in both directions, first fed wirelessly (is that a word???) from the cabin end then later wirelessly from inside the house.
Look at both your router manuals. If one can be set up as a repeater, this is all you need. Simply put it free-standing halfway to the destination. Otherwise run wire and drive the second one via wired ethernet.
Most phone wiring has two pairs and you may find an unused pair* that goes to your destination so you don't have to run new wire. 10mb ethernet runs fine on phone wire and 100 mb *may* run full speed on it. It's worth a try. DSL is only 1.5 mb so full 100 mb speed isn't critical.
About the only gotcha in using two routers is that the one fed by the modem is the master and it assigns IP's to everyone else on the network as they log in. The second router has IP-assignment turned off, and it passes-through the IP's assigned by the primary router. Its been a while, I don't remember the details, but I think you have to configure the repeater so it knows who is 'daddy'. And of course the primary router has to allow access by the repeater.
* phone wire trivia: traditionally the primary pair in a cable is Christmas colors, red w green tracer that is wound, twisted 1 twist per foot, with its green w red tracer twin. The other pair is Halloween colors: orang w black tracer twisted with black/orange tracer. I've also seen blue/white pairs etc. but this pattern of the primary wire's color used as the tracer on the secondary wire, and vice versa, should hold true. Dont use wires that aren't twisted pairs - the twist is important for noise rejection.
