Johnston generator rental service providers have different generators that can be rented at varying prices for your power source needs. A compact generator that can generate 500-2000 watts of electricity can be rented for $60 to $180 per day. A portable generator used for extended power outage can be rented for around $80 up to $250 per day, but can sometimes go as high as $280 to $300 for a model that can generate 3000 to 6000 watts of electricity. A larger portable generator that generates 7000 to 8000 watts of power can be rented for $300 or higher per day. A generator that can power an average size home can be rented for around $75 to $586 per day. Transportation fees may also add to the rental cost of a generator.