You can usually find a few on Craigslist, (search "all of Craigslist" for nationwide coverage). Basically price depends on overall condition, with rust being the biggest factor. I just recently sold my trio of 544 projects for
$1600 each. All of them needed floorboards & a few other minor rusted areas replaced. 2 of the 3 would run with gas & a battery, but were not driveable mostly due to brake issues. I had just made new upholstery for one of them, a'62 since I am thinking about making more to sell if anyone is interested. I used the old ones as patterns and wanted to make sure they fit, while I still had one to try them on. I'll probably buy another 544 at some point if & when I find the "right one". But first I need to sell my '68 122 that I have been restoring over the last several years, and finally almost finished.
It seems like most of the nicer cars are in California, but the prices are higher as you might expect. Above all, be patient. There is a market for vintage Volvo's, but it is a small market, so it could take a while.
Good luck on selling your car.