I did not sell my collection to buy original art, but at my peak, I had about 30 longboxes that were stored at my parents basement (my old room). When they sold their place to downsize, I had to purge since I had no intention of paying for storage for comics. I kept about 6 boxes of truly special comics, and the rest, I first sold the significant ones locally on craigslist (I think I only got $1 or $2 each canadian doing that) and when I was down to my last 10+ boxes, I sold it to a local guy in bulk who attend shows, I think I probably got 50 cents each at that point. Please note that these are mostly modern books.
I didn't sell to buy OA, but considering how much OA I buy regularly, you can probably draw a line that shows that cash went towards OA
Malvin