Call Glock and ask about the problem with the mag release. Ask if you can load a full mag and try to eject it, beat the problem will show up. In other words IMO it is worth $0. No point investing in something that is know to fail.
If you must have a ambi release look at the gen4.
There's a well used one at my LGS. What's a good price?
I purchased mine used and in like new condition and talked him down to $500 out the door. Even though he was a friend of mine, he brought the gun in on pawn for $300 and it was never retrieved so it was a win-win for both of us. Excellent gun and after shooting it I would have been more than happy to have paid retail on a new on because it is worth every penny.
On a side not the only thing that bothers me on this gun is the ambi mag release. For me it is not necessary and actually protrudes out far enough on the right side to stick right in the middle of my trigger finger. An easy fix by simply removing the mag release, taking the belt sander to it and popping it right back in.
In my case and many others, it was worth a brand new gen 4 21.
I guess the guys at Glock didn't like me! I got another Gen3 SF as a replacement. I just got it 2 weeks ago and the envelope date was 10-16-12 so the gun was brand new. It would have been nice to get a Gen4 but I am very happy with what I got. It has been flawless so far.