i.e. pay $5 to go back 5 days.
The time travel is permanent and one-way.
Edit: this is a one time offer and your budget is however much liquid cash you have right now. Cards are accepted, though.
For non-Americans, feel free to convert $1 USD to your currency
That’s actually an interesting point. You affecting the system will change the situation and therefore might have effects on the outcome. Might be minor like the value of bitcoin only varying by a small amount but it could also somehow cause Bitcoin to crash and never recover.
Same with the idea of investing all your money into a company like Apple. This could affect the development and decision process of the company and therefore cause them to fail.
So there is no guarantee for your actions to turn out successful.
Depends on the effects, one time theory I saw recently held that altering time was like a ripple or earthquake. The further you get away from the change the less effect you have.
So just going back in time wouldn’t stop 9/11.