AnotherGame is a mod for ToE 3.1.

In any normal tournament, without new versions of the game, the Tower faction was banned!

Yes, I was surprised. Apparently, they are introducing absurd restrictions even in tournaments. You would think that the Tower faction can help you win a game by forcing your opponent to attack with fewer forces and without scouting.

1000-2000? Heh. No one is forcing you to upgrade all mines.
Although, I was thinking of making it 5000 + 5 stone and 5 wood, but that's not quite right...
The price was not chosen randomly and was based on the lowest prices on the market + self-sufficiency.

What market prices? The cost of 1 resource is 100 gold, and a rare resource is 200 gold. This is a perfectly natural rate.
Based on the prices in the Capitol faction's upgrade tree, the investment should pay off in 4-5 days. Even based on the inflated resource values of 250/500 (instead of 100/200), your investment pays off in 15 days!

Added 6 minutes later
However, if you look at it through the prism of the exorbitant market prices, where only 1 rare resource is offered for 5,000 gold, your approach is appropriate. From a market point of view, no one will use this method to acquire resources that are not in high demand (I myself have rarely exchanged gold for resources, only for surplus resources).