If you have to redo the field, they possibly have to dig everything out, like 6 feet down or more, and replace it all with gravel and sand so it can drain, then lay down a new field. Ours was $12K to rebuild about 20 years ago.

It could be tree roots, which get in and clog everything. The field can still work even so, as long as there's some room to drain. We had a lot of clay in the soil as well as tree roots.

Suggestions: the less water you put in a septic field the better. And there are biotic products you can get to maintain the health of the tank.