There's absolutely nothing stopping third party candidates from getting their message out through the same channels that the main parties do. The problem is that people don't give a shit about the message...
Nothing stopping them
except the
massive resource disparity between the two main parties (and their relative stranglehold of major media outlets, don't forget!) and every flipping body else, and the fact that our voting system basically actively punishes the voters in most areas for not "voting for the right one" -- by giving their vote to people they didn't vote for, amongst other things.
Don't get me wrong, your last bits are absolutely accurate, that any attempt at getting a third party through will take that kind of effort, but acting like there's no other -- and no other
major -- barriers between a genuine third party attempt other than the effort is a huge misrepresentation of what's actually going down these days. I'm not even a "third party wannabe" -- I live in a state where it's only a half step from literally physically impossible for them to make in-roads rights now -- but that kind of message irks me, y'know? It's not "just get enough people together and working hard" -- it's "get enough people together and working hard in the face of massive opposition to any attempts to do so by the entrenched powers and the actual system itself."
And Misk, last I checked no one's been elected by an actual majority (let's go with 2/3rds and make it easy) of the whole population, or even the total
voting population, for a long, long damn time. The folks that have been getting voted in are doing so generally scraping in
barely a slightly larger
plurality of the voting population. And yeah, yeah, you can say "well, people don't give a shit or whatev' so they're not voting" but I'd say that does a pretty damn huge disservice to a lot of people that don't or can't vote. Not all of them, no, but a lot of them.