@pumpkinkangaroo That's an interesting idea for sure! I would say one thing, this kinda removes the freedom of when to buy the stock. I think at least 1000g is a good idea, my prices were way too low, but if you don't want to buy them at the beginning then see an opportunity to later on I think that should be an option, but maybe it's an option you have on a timer as I suggested earlier.
The reason I say this is I think it would be fun to have the freedom to do that if you suddenly see something you want to do and want to boost your stock for it.. voyages you don't tend to need a huge amount of stock, but if an AI threat spawns (the kraken, we have no idea how the new AI threats would function.. perhaps they need quests, or perhaps they are spontaneous like the kraken!) and you need more stock then you can do this... I think this would also go hand-in-hand with the fact that people are asking for unique rewards from the Kraken. If you wanted kraken-related cosmetics, titles or whatever the reward is, there would be incentive to spend that 1000g if you needed more stock..?
Likewise if a fort becomes active but you have just sailed away from your outpost, you could think 'ah actually, lets stock up the ship and then go and have a go at this fort!', then after your purchase the 'restock' button is unavailable for an hour or so.
I like your husband's suggestion regarding the price, and the amount of stock which can be purchased though. Perhaps there could be additional restock options to choose from which cost the same and ALL are on a 1 hour timer (so for instance, you have 4 options, you can choose 1 of these options each hour.. per crew member)
The options could be:
A bit of everything: 10 bananas, 20 Cbs, 10 planks
Bananas: 35
Cbs: 40
Planks: 30
Just random figures I plucked out, but the idea being if you know you are fine with bananas you have the option to just buy cbs, or just buy planks etc :)