> There is no such price, because there is no way to sustainably develop a product without subscriptions

Such a price clearly exists -- in an extreme case you could charge 50x your annual subscription price and invest it with a 2% yield to get the equivalent of your subscription as interest. More realistically, if you are already considering taking on debt to grow your business it can make financial sense to offer lifetime licenses that are equivalent to several years' worth of subscription revenue to get an influx of up-front liquidity. Of course as your needs change so will your ratio of subscription-to-purchase price and this may result in a purchase price that is too high for your customers to consider, but the number always exists.

> Every one-time price is a gamble

True, but so are subscription prices! Either way, as the person who sets the prices, you are well-positioned to pick ones that are most likely to be successful.