What is a difference between a WiFi extender and a second router?

[GreekTzatziki]

I have a router which is connected to my pc in the first floor and covers with wifi only the second floor. I want to install a pc in the third floor for movies etc. but I have a poor Internet connection there (1-2 bars). I considered buying a WiFi extender but the signal might not be as good as having the access point next to me. So, can I buy a second router without paying more money at my telephone company for making a second connection?(I don't know a lot about this stuff so please forgive me for mistaken terminologies.)

 

[Kestas0]

Why wont you just run a cable to third floor? if you want to plug second youter next to you woulndt it need cable enyways form your first 1?

 

[sizzling]

How about power line adapters?

 

[GreekTzatziki]

How about power line adapters?

Actually, I found out that I can plug an ethernet cable straight from the wall. Thank you by the way