betfair prices. can easily get several grand down around the price.
50 % return on investment over a year is pretty good imo. Lot of money in bank accounts making 3.2 % over the same period.
You aren't getting 50% return on investment though. You think he is a genuine 1/3 shot and he is available at 1.6. So your expectation is 75% (1/3)*1.60 = 120 so you only actually make 20% on your money and you are getting 6.7% compounded over two years without the variance. That is without taking into consideration credit risk, Betfair commission and the opportunity cost of the short terms bets you could make with the same bankroll etc.