well, depending on many diffrent variables as many of your fellow comunity members stated above,
botting being a very important one, if the account has ever been botted or not
first owner is one i always want to know when i buy an account, to risk recovery tricks
stats depending on the dificulty of the 99 id say 10$ to 25$ per 99
cash value i generaly guess about 0.4$ a mill if they have a substantial amount, if not then its just left out