I wouldn't call it a bargain at a 5 relative to other sports for any card not made in the 1950's (or before) unless we are talking about Jordan and a few others who certainly transcend the sporting world and pop culture more than Steve Austin. A 5 is a very ho hum grade for a modern card (even though I've seen 5's that could pass for 9's but for an almost invisible surface flaw through the PSA holder). To get a graded 5 card of just about anything made form 1990 forward that's not autographed or serial numbered to sell for a 150 is remarkable and shows you how dedicated wrestling card collectors are becoming as well as how scarce tha Austin is perceived to be in any grade.
I think that Austin 9 at 600 is looking more and more like a steal of a lifetime as I don't know that we will ever see another one even close. I think someone could double that now if it were to come up for sale again but I could be wrong.