Math time:
20,000 switches at 16 cents each = $3200 per colour.
At 24 cents per switch, we'll be spending the same amount at 13,333.33333.... switches.
Therefore, assuming equivalent shipping costs, and no intermediate price breaks, it makes sense to scale up any colours at 13,333 or more switches up to 20,000, even if it means giving everyone more switches than they ordered, or using the extras for a giveaway or raffle, or just dropping them from a great height and filming it for YouTube.
The media response would be hilarious: Traffic ground to a halt downtown today, as pranksters tossed thousands of tiny mechanical switches into a busy thoroughfare. Homeland Security has adjusted the Terror Alert Level to Gateron Black in response to the situation.