When I see "firewood" and "brush" separated, I think "brush" is anything less than about 8" in diameter. Everything above that is firewood. A big log like that is, by far, the most expensive/difficult piece to remove. If you really want it gone, them willing to come back out for $500 seems pretty reasonable.
If you wanna see if you can get it sawn up instead of firewood, that may cost you or you may find somebody who wants to pay for it. A big saw mill doesn't want to deal with one log. A small saw mill may have trouble moving one that big. Smaller sawmill might want to buy it...or might have you contract with them to saw it up (it will cost more than $500...but you'll have the lumber).
To go that route, couple of thoughts:
1) Ask the removal company if they have any contacts they know might want it
2) Contact ODNR Service Forester to see if they have a list of small/portable mill operators who would be willing to deal with one log.
https://ohiodnr.gov/discover-and-le...dnr/forestry/contact-us/aab-service-foresters
3) Contact Ohio Forestry Association to see if they have any members they know of who would want it...generally their members are larger mills, but worth a phone call
https://www.ohioforest.org/page/contact