I had a good XP with urban-rentacar.com 7 months ago.
Paid 1000 pesos for 4 days (unlimited mileage), for a small Chevy with a 1.6 liter engine (better discard any 1.3 liter engine if you intend to drive in the province = far too dangerous to pass other cars with a small engine).
When I gave back the car, I asked them if I could rent a car on a monthly basis, renting one towards the end of its lifecycle and they actually had one, a Ford Ka from 2007 with the AC not functioning and a few issues. I negociated a deal of about 2500/3000 pesos per month but didn't follow-up finally.
As of now, best deals you can find run around 250 pesos per day (or a bit less with a limited daily mileage).