$300 isn't a bad price, but finding S&W magazines for the Model 4516's is becoming a quest. I haven't seen any new magazines for the 4516 in a while, used one's go for $50-$80 each. Promag makes new ones, but they are junk in my opinion.
I have a 4516-2, it works fine, but I wouldn't say it was enjoyable to shoot, its pretty heavy for a single stack. The 4506 would probably be better, but you won't find one of those in the $300-$400 dollar range.