Avoided reading the rest of this post for the spoiler warning, started the interaction on the blog post, was bothered by the money question since how much I'd be willing to pay is directly related to how much money I have/make. (If I were willing to pay as much as $250, I'm doomed financially. If, on the other hand, this is how much we're willing to pay with a guaranteed conscientiousness increase, I'd expect to make back what I paid in the first month.)
I wrote an interactive blog post, How To Increase Conscientiousness, which has some steps which I think might increase your conscientiousness. I'm not sure if it works, but I would love to see some curious low-conscientiousness people try it and post your results here.
If you do it, please do it before reading the comments on this post, as they may contain spoilers.
If you are feeling especially helpful, also take a Big Five personality test like this one and report your percentile result on Conscientiousness.