The materials and installation is around here is usually around $2800 to $3500 for a standard system and up to $5000 if an aerobic system is needed because of ground conditions. 

Wow the most I have ever paid for a septic was $6500 for an aerobic system. 

If you have to have it pumped, then the anaerobic bacteria level has been to low for to long or people are throwing things in the toilet that they shouldn't.

If you have rock or in a hill type environment, you'll need an aerobic system which cost 10-15k.  

In my state, they require a permit (additional costs), and estimates can range from $2,000 to $20,000 depending if the system is anaerobic or aerobic!

https://www.walmart.com/ip/Pee...our system has two conventional tanks from more rhan 30 years ago which was connected to an aerobic tank 20 years ago.

with a septic tank you need to budget in pumping cost and with it being a rental I suggest pumping every 3-4 years. you also need to limit the amount of bleach products you use because it kills the anaerobic bacteria that makes a septic system work properly.

It does have an aerobic septic

As others have said it sounds like a system that needs to be pumped or possibly a crushed line to the leech field if it is a standard system or damaged pump or heads if an aerobic system. 

For example, in China, low tech anaerobic digesters have been in small scale use for 100's of years.