Buy an ethernet extention cord as well as another router. Then connect the cable to both routers and put the new router as close to the place you want the signal to be recieved at.
If you want to be reassured, it's how you can access the same network from hundreds of feet away (at a school or a library). They have several routers set up everywhere.
I've heard the best way to extend your router range is getting a bigger ariel. Try getting a 9db (or something like that ) ariel and put it on your router. Try getting one off ebay as it will be much cheaper than getting it from a shop.