sublet fee

Seems way too high
Should be 25%-30%

Look at your house rules. My building escalates fees yearly to discourage rentals.

Your co-op board had made rules that discourage residents from heading down the path of turning the building into a hotel. They should be encouraged to forbid all rentals.

Below is not legal advice, just some thoughts based on my own understanding of the issue. The gist of it is that a coop board is able to make and enforce this kind of rule as long as it is applied equally to all shareholders, and this kind of rule is likely in the interest of shareholders.

The coop is looking to maintain the number of resident shareholders above a certain minimum threshold in order to fit within bank lending rules to make is possible to obtain mortgages on the property. There are two kinds of mortgages to consider: the building might have a mortgage, and shareholders have mortgages on their units. If the number of units in the building that are rented out exceeds a certain threshold, obtaining a mortgage becomes more expensive or even impossible, and the values of the units drop, as the units can only be sold at that point to all cash buyers, which is bad or any shareholder looking to sell. Plus, the coop might not be able to refinance its mortgage on the building, which means when loan becomes due they might need to assess shareholders for tens of thousands of dollars to pay off the loan - also very bad for the shareholders. When buildings do not have too many renters, many boards maintain a more liberal policy, allowing shareholders flexibility if life circumstances change, temporarily. But as the number of rented units gets closer to the threshold, the boards often adjust the policy, to encourage people to stop renting out units.

If you are not planning to live in the coop apartment in the future, it might be best to just sell it. Coops are not intended to be investment properties.

Interesting ideas