If its only a couple days, it comes back in the same condition it left and with the fuel tank full, I wouldn't bother charging him IF he's a good neighbor and not a burr under the saddle kind of guy.

If its a couple weeks or months, that's a different story.   IA State custom rates for snow removal (loader) range from $70-$150/hour with an average of $106.       That obviously includes fuel and an operator so adjust accordingly.   

Otherwise, tractor rent ranged from $.26-$.38 per horsepower/hour with an average of $.32       What that means is if you have a 200 hp tractor x $.32 would be $64/hour to rent it.   But that would be tractor only, no loader.