As someone who lives in Exeter the Chiefs have the benefit if drawing it's support from the whole of Devon, Cornwall and some of Somerset. Top level sport is thin on the ground here so people will travel to watch it. Exeter, Torbay and Plymouth are no richer than anywhere else but there's enough money in surrounding areas to make the scheme viable.
The Chiefs make the whole day an event as well and there's hardly any pubs nearby so the money they make at the ground is huge. It's also situated perfectly on the M5 for conferencing.
The football team which is owned by it's supporters average about 4k and the support has held up well despite the Chiefs success, I know a few people who no longer go to the rugby because they have alienated them and priced them out of going.
Hope that clears up the geography. I've never set foot in the place even when offered a free bar.