  In exponential semi-martingale setting for risky asset we estimate the
difference of prices of options when initial physical measure $P$ and
corresponding martingale measure $Q$ change to $\tilde{P}$ and $\tilde{Q}$
respectively. Then, we estimate $L_1$-distance of option's prices for
corresponding parametric models with known and estimated parameters. The
results are applied to exponential Levy models with special choice of
martingale measure as Esscher measure, minimal entropy measure and
$f^q$-minimal martingale measure. We illustrate our results by considering GMY
and CGMY models.
