What is the right tool to cut this PVC pipe?

[dmjlambert]

You folks that are handy with landscaping and ditch digging may be able to help me here.

This big pipe is 4 inch fairly thin-walled yard drain pipe. I am re-routing it. I need to cut out a section of it, and then I will no longer use the section that is going off to the right. I will connect a 45 degree elbow on the section going off to the left and lay new pipe in my new empty trench.

What is a good thing to cut that big pipe with? It is in a somewhat tight spot and I need to leave the smaller sprinkler pipes undamaged. I would normally just use a hacksaw, but that is only an option if the pipe were much more accessible.