You can't. The internet isn't a "thing" you can hold in your hand.
You could buy a router new for <$50. Thrift store, maybe $10. If they have them.
You'll also need to *rent* an internet connection. How much this costs will depend on where in the world you are, how fast/how much data, and what type. The cheapest are certainly under $80 per month, likely much much less.
And finally, there's the actual PC you use the internet on. That could be $300 for a new one or a cheap laptop. Second hand, likely <$100 but you'd need some setup work.