You have your terminology confused. The companies that you mentioned manufacture routing equipment that allows several people to share data (including the internet). With respect to access to the internet, you need an "internet service provider" (ISP). Wether one is available depends on where you live. Some areas have several ISPs that you can choose from while other areas only have one (or none). Kind of like Sony or Samsung. They make TVs but they don't make the TV shows.
i dont even know how i should answer this question .... wifi as in a connection is free -the electricyty used by the wirless router... you should look up isp in your area for the cheapest service providers . wirless routers vairy in price depending on what you need /howmany ports/what frequencies you need b/g/n