Why would that be expensive? Most say 3500 to 5k. Bali An is a bit pricey, but it's worth it. There are many wonderful cheap hotels though.
Bali Island, not too far away, is a bit cheaper.
I think Bali An is expensive because of it's location. In fact, being in a more visible and accessible location, tends to bump the price up a bit.
Expense
For short stays, I find the prices to not be an issue. 3,000 or 5,000; as long as it's nice. But I understand that if a guy just wants 1 hour of "hit it and run", then a cheaper spot is as good as any. Prices are murder in Japan. Maybe a roach or the smell of garbage will add to the ambiance.
It's those overnight stays that are the true killers in my opinion. Particularly when they have that after 9 or 10pm rule, where you must pay for overnight. Hotels get slick too, where they jack prices up or only have the most expensive rooms left. Can be cheaper to take her on a 4,000 to 5,000 yen taxi ride back to the apartment, then deal with hotels.
The hotel, by itself, can be 12,000 to 25,000 yen. Not even talking dinner, alcohol, and entertainment (often easily at least 10,000 yen). Even if your lady is paying 1/3 to 1/2, the sting can possibly be felt.
And if you paying a woman 20,000 to 40,000 yen (plus any extras like dinner) then that can be a huge expense as it ticks past 50,000 yen.