Die grinder is about throughput. I guess you can make that up by storing a hundred gallons of air. Certainly cheaper. It probably failed because the guy raiding it for parts let the oil out. At least, I would consider that a keen possibility and recognize that the rod isn't the only part to fail as a result, just likely the first. A 7hp replacement pump looks to be about $750. That kind of money gets you big boy toys. I would save the motor, take a zipsaw to it and put it in the recycle bin.
There are only about 4 other moving parts in the whole compressor, and they're all in good shape--no axial play at all. A new con rod and one crank bearing (that I need to remove to install the conrod, plus it has a wee bit of wobble to it) is under $50. I think I can deal with that. I can replace this pump new for about $300...$750 would get me into a very nice 2 stage pump. I'd love to do that but I have other things to spend that money on...