I just made a random guess of 3.500 for a 200k arena and 7.500 for 500k arena. And the numbers are a bit depressing.
When do you turn profit?
200k Arena - 58th week
500k Arena - 67th week
1m Arena - 85th week
2m Arena - 127th week
4m Arena - 169th week
How long does it take for the more expensive arena to turn more profit than the less expensive one?
200k vs 500k - 76 weeks
1m vs 500k - 114 weeks
2m vs 1m - 252 weeks
4m vs 1m - 253 weeks
So if you build 1m arena it gives you more profit than both the 2m and the 4m arena for 251 weeks.
On the other hand it would be nice if we had the correct income for the 500k arena.
Just by changing it from 7500 to 9500 makes it 208 weeks for the 1m to turn more profit than the 500k. So small changes make a lot of difference here