Were I looking for one, I'd willingly pay $500 for the gun in the photo.
I bought several back in the early 90's when they were going for $250-$299.
I recently saw a barely gunsmithed example for sale in the Denver area that vaporized within 30 minutes of being offered for sale. It had been refinished (bead blast & parked), springs replaced, and generic Hi-visibility (Brownell's catalog) fixed sights added.
$650 asked and gotten quickly on Armslist.
I've seen a nearer-pristine pistol (original finish in NRA Excellent condition!) swapped for $800 cash about two years ago. That particular gun had seen little duty use and probably resided in some senior officer's desk for decades.
They are fine guns (I still own a pair) and deeply appreciated for their old-school quality of manufacture and functional reliability. As eventually happens with nearly all milsurps, the prices for original (unmodified) examples are now surpassing the prices of all the specimens that were "sporterized".
They are about as close as you can get to an all-steel, Colt/Mil-Spec tolerance, no MIM/no plastic 1911A1 without spending three to four times the amount for a comparable GI gun or pre-war Government Model.
Deals can still be found, but they are rapidly leaving the ~$450 price point behind. Lately, I've seen a few really ratty ones offered at gun shows for up to $650...with no takers (for now). Nevertheless, in another year or three, they will fetch that amount. Kind of like Walther P-38s do nowadays.
I've yet to come across a Sistema that had its original (serial numbered) magazine. The odds of original magazines remaining associated with the guns were severely diminished by decades of police & military arms room issue procedures. No biggie. That's such a normal and expected occurrence that it doesn't detract from the price on Sistemas. On the other hand, having the original magazine would certainly add a few bucks in value.
Inexpensive Sistemas were sleepers for years (like CZ75s used to be)...but no more.
That's a nice gun in the photo. I'd get it and leave it just the way it is. For $500.