No fixed threshold exists. What matters is the ratio between the money committed and what it genuinely costs to establish a laundry of this size, so the question is what share of that cost is already spent rather than whether some headline number has been reached.
Proportion of the real cost
Hypothetical example: a Hampton couple are given a minimum figure by an acquaintance and conclude that a laundry could never justify it. The measure is a ratio, not a floor. If setting up a plant of this capacity genuinely takes a given sum, then having spent almost all of that sum weighs heavily in the couple's favour, and a cheaper undertaking simply has to show a larger share of its cost already gone.
Claims are weakened by padding: working capital nobody has committed, a truck that stays in the family, projected outgoings backed by no invoice. Count instead the rent paid, the machines bought, the fitting-out billed, the permits, the insurance, the opening stock of linens and chemicals. Charges for the application itself are set out by the government agencies handling it and should be looked up rather than remembered.