You could travel to an extrasolar planet - but you wouldn't get there alive!

There isn't enough energy available to get there in a human lifetime, and generation starships suffer from competing design flaws: measures to minimize outgassing compete with measures to enhance heat loss. These three aspects taken together mean that it is impossible to travel to the stars (and get there alive). There is only a minute chance that someone will find an optimal combination of technologies that can get us there. It won't happen in my lifetime though.

Note that any ship that would carry humans to another solar system would have to be a generation ship, unless it is capable of a round-trip in less than a human lifetime. Otherwise it would have to re-stock on whatever resources it finds there, and keep its passengers alive indefinitely. We couldn't expect a planet like Earth. We would be lucky to find a planet that we could land on, and an atmosphere that we could insulate ourselves against, while we harvest minerals and volatiles, and setup our robot factories.

IMO it all amounts to a small set of impossible-to-solve problems. Cost and economies of scale aren't really even worth mentioning at this point.