Yes you got one of the rarer chamberings in the Savage 99. I managed to pick one up myself a few years back in very good shape. It would be easier if we knew which exact model of 99 you have like mine is a Savage 99A which is their "brush gun" style. This is what my rifle looks like:
I've seen a few .358's on Gunbroker most of them start around $1000 and go up from there depending on when your rifle was made. I'm not a 99 expert by any means but there are some years more desireable than others.