Well, either he has no clue what the guns are worth relative to each other and believes that a .44 Mag must, by virtue of being a larger caliber, more expensive. If this is the case he needs a reality check. Or, he knows full well what the guns are worth, thinks you don't, and is trying to screw you over, which makes him not much of a friend. Either way, it's NO DEAL unless you like getting rooked.
I actually had to read the post twice because my brain wanted to think that he was offering BOTH Taurus' for your gun and 200 rounds of ammo. That would be a more equitable trade given ammo prices these days.
Again, I'd politely decline his offer.
Mike