1) How good is your existing router? Just getting a modern AC router can extend your range tremendously without the need for an extender. The TP-Link Archer A7 is just terrific and not expensive; for a little more money look at the Asus RT-N66U.
2) Look into powerline extenders. They're cheap and effective -- BUT they need to be on the same branch of the electrical system to work. So if your wiring allows, you put one powerline extender where your modem is (where the internet comes into the house), and another powerline extender in the middle of the house somewhere, and then connect your router to the second powerline extender.
3) Option 3 is a wifi repeater though it will reduce your network speed somewhat. Netgear N300 plugs into a socket for about $35, and TP-link makes for about $20 that works well for most people. At that price you try it out, and if it doesn't work, return it.
But unless you have a huge house with lots of masonry walls, a really good router should be able to reach just about every room. We have the Asus (provided free by T-Mobile btw) and it goes from the basement through lots of masonry to the 2nd floor on the opposite side of the house with just tremendous speed and reliability.