At Harbor Freight they have a 120 volt electric impact. They work amazingly well for what you are needing. I know you said that you don't want the extra expense, but it would be cheaper than an air compressor, and pneumatic impact. I love mine, and have found a lot of uses for it. I originally got it for changing the mower blades on my garden tractor.
Don't forget to soak that thang with the PBlaster