[Bear_Slayer]

Use a Skil saw to plunge cut most of the material out of the middle. Then go through with the sabre saw to remove the rest of the material.

[tacticalogic]

Depending on how much waste there's going to be you might want to do that.

If I understand the situation correctly, rudy45's availble selection of tools suitable to the task is limited to a borrowed jig saw.