What caliber?
No key is the way to go.
I got mine brand new for just over $800 (stainless synth).
All depends on the gun - caliber? Stock? W/rings?
The Optilock rings retail for like $120 so that makes a big difference. Even the lows will mount a 50mm bell (up to 58mm
http://www.sako.fi/mounts.html). I hav no idea why the optilocks are so damn high. I love them, but they're too high and can be hard to get.
IMO, Sako makes one of the best "out of the box" rifles in the world. I have a stainless synth in 7mm, and will soon augment that with a delux-stock blued model, also a magnum.
You'll be quite happy with it whatever it is.
Check out Ebay for mags and accessories. A guy by the name of Ridgerunner sells a lot of Sako stuff.
Enjoy it.