$100 for a new lock. Installation is not complicated. If you can assemble an AR lower, you can install the lock.
If that's what it needs, it's not a bad deal, as that's close to a $2K safe when new. And remember it's craigslist...that's an "asking" price. But.... I'd have to see a picture of the inside of the door to say if more was needed. There could be more to it. That model does not have an external relocker, it has a very heavy steel backup plate behind the lock instead, to prevent lock punching. VERY heavy plate, almost overkill. And very good hardplate in front of lock. Quality safe from top to bottom.
Something's not right about that picture of the front. There's 3 holes between the dial & handle. That's the typical mounting hole footprint of how the dial would be mounted on the door. 10-32 tapped holes at 12 & 6 o'clock secure the dial ring to the door, then the dial spindle would go through the large hole. But the large hole looks too big, and the smaller holes are too far apart. And all 3 holes are too far to the right for the lock to have been mounted there. There are safe drilling rigs that use the same hole pattern as what's on that door. I can't say much more on a public forum.
If any of you guys are interested in it, ask for a few pictures of the bolt works inside the door in the area of the lock box & door handle, and post it here, or send it to me in a PM.
https://www.amazon.com/Sargent-Greenleaf-6730-100-Safe-Lock/dp/B01MQMM72A/ref=sr_1_2?crid=3LNWIJM10G4R3&dchild=1&keywords=sargent+%26+greenleaf+s%26g+model+6730&qid=1588679880&sprefix=sargent+%26+greenleaf+%2Caps%2C217&sr=8-2