Ok, I get the offering a reward part. And I get they're probably not made of money, obtaining these funds through grants or private "loans" that may or may not have to be paid back...
But $500? For a $130,000 machine? Obviously if some random fisherman finds this and realizes it's worth $130,000, they may take their chances on trying to fence it.
Wheras if they offered say... $5000, or even $3000. Then I'm sure said potential ransomer would find much more incentive to be a good samaritan about the whole thing and just go for the no fuss $3-5k.
$500 is a nice chunk of change sure, but it's not even a mortgage payment, hell barely a monthly car+insurance payment. Give people a reason to turn it into you, and consider it a cheap lesson in redundant locator systems.
By the way, I know for a fact that some people would return this without even asking for ANY reward, but there are far, far more people that would consider ransoming it for as much as they possibly can.