Squirrels chewed up the wiring and insulation throughout the attic space.

Question - what is the most efficient/affordable method for insulating a garage yourself?

Then spray foam insulation in holes to prevent rodent entry into the wall.

My first required very little work,  but the contractor I used said he could re-insulate, rehang all the drywall, and replace the subfloors for about 28K.  

Since we were not doing any site work, we installed the pump and tank system, along with a fire alarm system.We also needed to get spray foam insulation installed in various areas and with the extra demo, we now had to board and plaster even more of the space, as well as replace the blown-in insulation that was lost.The final delays towards the end of the project were mostly related to some quality issues from the prior three carpenters and plasterer, so add another few weeks there!

Is one room an addition and so might not be insulated as well?

New insulation and sheet rock along with roof and paint.

I want to control the whole area and tenant base to insulate my investment.

Insulated attic.  3.

I would definitely be removing some drywall, if only to see if the mold is on the side of the walls/in the insulation.