We study the function evaluation problem in the priced information framework introduced in [Charikar et al. 2002]. We characterize the best possible extremal competitive ratio for the class of game tree functions. Moreover, we extend the above result to the case when the cost of reading a variable depends on the value of the variable. In this new value dependent cost variant of the problem, we also exactly evaluate the extremal competitive ratio for the whole class of monotone Boolean functions.