I'd be cautious if your estimate goes higher than an hour per axle, less parts. Hourly rate could be $100 per hour. I would suggest grease seals be replaced, bearings be solvent bathed, blown out dry then inspected for scoring and over heating. I am a big fan of synthetic greases as they stay viable a lot longer. Remember a too tight bearing will overheat and fail quicker than one set with the proper preload! This service is not rocket science, however it is becoming rare with the adoption of cartridge type bearings that require zero investment during their useful life, aka nevr lube hubs/bearings.