the ones available thru autozone are usually anywhere from $17 - $250. most are in the $17-$30 range.
chevettes cores, caprice cores, bonneville cores are all under $20.
$250 is prolly not the most expensive but it is the most expensive that I have ran into -- and h311 no, I didn't buy it. If I wanted to spend $250 for a rad, I'd get that big honkin' mirror-finished F1.
you could probably find them cheaper than $17 if you looked but you might end up with a leaky core...