If it's just the mag, for example David Odess http://www.david-odess.com/repair.html charges $90 to CLA an A-12. If it's the bod, $195. OTOH, a replacement/additional mag at KEH that comes with a reasonable warranty and replacement runs anywhere from $39 to $235. http://www.keh.com/Camera/format-Med...c=80970&r=WG&f
Spare mags are always really good to have as you've just discovered and gone are the days when used ones cost nearly as much as new. If you're on your own and have a repair shop in mind, I'd send the whole rig in for CLA. I say that because it's possibly the body gearing.
If you look at the back of the body, on the right you'll see the gear mechanism that couples with the mag. If that gearing is worn it'll cause the mag to either jam or skip frames. Just the same as worn gears on the mag will cause the body to jam. Hard to isolate even test firing and cocking the body without a spare mag that you know is good.
Nonetheless, welcome to the party. I'm sorry this happened to you right out of the gate. It's a truly great piece of equipment and actually remarkably durable. It's probably an easy fix but the labor is awfully pricey and don't try this at home. Light traps are easy. Mag and body gearing is a little different.
Take it light ;>)