In this situation I can see it costing more. And to the post where it was said they use the same vehicle to tow as for towing a car, that’s not necessarily the case.
First, if the bike’s forks were locked, it’s no longer easy to push the bike up a ramp. The bike would have to be lifted onto the tow vehicle. That’s at least a 2-man job, unless it’s a 50CC trials bike and in that case one strong man can lift it. I’m guessing the OP’s bike is not that light. Most are in the 300-600bs range. Second, the tow vehicle needs to have a flat bed or dedicated motorcycle trailer or tow setup. Getting a dedicated motorcycle tow trailer to the tow site is an extra cost.
Second, you need good straps to cinch down and secure the bike. Typically four straps of the come-along variety. The straps have to be attached to the bike carefully to avoid damaging brake lines and such.
All this takes quite a bit of extra time, not to mention expertise. Not all car tow drivers know how to secure a bike.
So, yeah, $500 is understandable. Ouch, yes, but understandable.