Seats are big and heavy. Shipping them anywhere is going to be expensive. So your market is mainly local. That would call for something like Craigslist rather than eBay.
The price depends on the size of your market and how quickly you want to sell. The smaller your local market area and the quicker you want to sell, the lower your price is going to be.
For example, I'm in the greater Los Angeles area. There are something like 5 or 6 million people living within a 2 hour drive from me. That's a big market. Because of that, there are a couple of people with constant ads on Craigslist asking for $1200 a seat. They also appear (from the photos) to have a warehouse to store seats, so they're not in a rush to sell.
On the other hand, there's someone like me. I listed my seats here and on Craigslist. In spite of multiple inquiries through this site, I actually sold them to someone local through Craigslist. I didn't have the time to wait, nor did I have the space to store the seats for any length of time. So I was happy to accept less than half of that from someone who could pick them up. Still, it took about 3 months to sell them.
If you're in a more rural area, I doubt if you would get even that unless you're willing to wait a very long time to sell (as in a year or two).