The plug adds yet another variable, another chance for failure on a critical part of your safe riding.
I am with OND, I would only use a plug to get me home from an immediate trip and then the tire goes in the scrap bin. My life is literally riding on that 2"x4" contact patch, I wont take the chance on anything that could possibly increase the chance of failure.
As for used tires, assuming that it is not plugged/something wrong with it, there shouldnt be a problem but I wouldnt buy it from ebay or someone you did not know.
My advice would be to check with your local racers for takeoffs. Most of the time you can get them cheaply. I charge $50 for mine with 50% edge wear left and 95+% center wear left, some go much cheaper. If you ride primarily on the street you are generally only using the center of the tire which is practically brand new on a race tire.
You can also check for deals at local tire places and look for closeouts at shops like sportbiketrackgear.com, etc.
It sucks for sure, and I know well what it is like to be tight on cash but ask yourself this: If you cant afford a new tire, can you afford hospital bills?
