Ideally you want something that can nicely go from 10,000 to 30,000 seat capacity.
The lower end being for Cavalry and Wild. The higher end being for Grey Cup, a big soccer match, outdoor NHL game and a big concert which would actually have higher capacity because you can use the field.
There are a lot of simple designs out there that can be pretty basic, which is all we need. Best comparisons are probably MLS stadiums...
en.wikipedia.org
Cincinnati
26,000 Seats
Opened May 16, 2021
Construction cost $250 million (343.75 million Canadian)
View attachment 666756
en.wikipedia.org
St. Louis
22,423 Seats
Opened November 16, 2022
Construction cost $457.8 million (629.48 million Canadian)
View attachment 666755
en.wikipedia.org
Austin
20,500 Seats
Opened June 16, 2021
Construction cost $260 million (357.50 million Canadian)
View attachment 666754
en.wikipedia.org
Columbus
20,371 Seats
Opened July 3, 2021
Construction cost $314 million (431.75 million Canadian)
View attachment 666753
So with a 2025 budget of $500 million Canadian you could probably get something like one of these. You could probably cut out a lot of bells and whistles (roof, permanent amenities, etc.) to maybe get it to $350 million Canadian. That doesn't seem crazy expensive to me. Especially if you put a bubble on it and call it a community recreation space from Mid-November to Mid-April.