If the rifle is in excellent shape then you got a good deal.
5.56mm ammo is going for around .40c a round, so that's "around" $32 worth of ammo.
What would throw your deal into the real of great deal would be if that 30rd magazine is a Ruger factory Mag. They go for around $100
The Ruger Mini 14 is a nice rifle >Mine must be defective also, because that's what I get 2 - 3 inch(5 shot) groups. And no that's not iron sights, I have a Weaver K-4 on the one I shoot<
I have to confess that I do prefer the Colt AR-15(SP-1), but both are really nice rifles.
You can check and see what one in like condition to yours has sold for recently on
http://www.gunbroker.com >use the "going-going-gone" feature to search what they have sold for in the past 90 days
http://www.gunsamerica.com
would be another place to check and see if you could find one in similar condition to yours.
I figure, if I'm happy with a deal and the guy I bought if from is happy, then it was a good deal.