Monthly means you can start renting when you need it. Stop when you do not. Start back up if new work shows up.

When you need it, never when you do not.

But if I may ask if you don't make enough for the monthly rentals how did you plan on paying for an outright full purchase?

Or is this a "bought AutoCAD 20-years ago and now it doesn't work now and I'm looking for a free fix" type posting? In which case there are still free to use CAD programs out there that pretty much still look like AutoCAD from 20-30 years ago, lots of low-earnings folks use them successfully. They are just not from Autodesk. Explore them and break the chain, be free.

HTH