The 74 Roadrunner I bought started at $5,000, then went to $4,000, then $3,000, and I bought it for $2,000.
If he's dropped that far, it's likely because he either wasn't getting any serious buyers, or little or no contacts at all, which makes sense as his prices were pretty high. The guy I bought mine from was tired of hearing from people who said they were interested and wanted to see the car, but then they never showed up. He told me I was the first person who actually had.
The approach I would take with the guy is:
A. If the car were a 72 or older, you could name your price, but 72 is still considered the end of the Muscle Car era, and 73 and older cars just don't command the prices the 72 and older cars are getting.
B. Fully-restored 73 Roadrunners are barely bringing in $10k in most markets, and that's with big blocks in them. This car is a Satellite with a 318. Even in fantastic shape it's only worth about $5k to $6k in today's market, and this car isn't close to fantastic shape.
C. You've got rust in the rear quarters, which is the death knell for these cars since no one is making reproduction quarter panels, and every year that goes by, there are fewer and fewer 73-74 cars to restore so there's no way anyone's going to start making replacement panels. That means I'm going to have to buy OEM sheetmetal to fix those quarters, and that costs a small fortune.
BTW, this is likely a reason why the car hasn't sold. Those quarter-sized holes in the quarters are just where the sheet metal has fully rusted through... not where all the rust is. Quarter panel rust has been a serious issue with 73-74 cars for decades, thanks to the poorly designed drainage holes in the back of the car. They quickly got clogged with dirt, pine needles, leaves, etc., and allowed water to back up and rust out the quarters. I'm pretty sure if you start feeling around those holes, and looking at the backsides of the quarters, you're going to find a lot more rust damage. If you do, my best advice to you say "thanks for your time' and leave. Yes, you can buy some replacement sections for the quarters, but if the rust is very extensive, you're going to be paying more for bodywork than the car will ever be worth, and there are too many nicer 73-74 Sats and Roadrunners for sale out there to blow through a ton of cash fixing up a rusted out 318 car.