A Farro Fresh spokesperson explained the watermelon was out of season and had to be shipped from Australia.
It was also a 10kg whopper - 10kg of tamarillos from Farro Fresh (at the current $25/kg price) would set you back $250.
Turnbull said if we are stuck in our ways and want to eat the same food all year round we will have to fork out the cash, get used to eating carrots, or adapt.
"Historically we used to eat seasonally but we have become so used to being able to buy what we want," she said.
"Now if you want to keep eating that tuna salad through winter you are going to have to pay for it."
Turnbull said people would be in for more price shocks such as the $100 watermelon if they wanted to buy out-of-season - but they didn't have to.
For those stunned at the price of the 10kg fruit (that is best enjoyed dribbling down the chin in the hotter months), there are plenty of other options.
"It's about getting a bit creative with your recipes and knowing you can swap similar ingredients," she said.
"One easy swap is courgette for green beans so if one of those is expensive or not available then go for the other."
Turnbull also stressed the hero of out-of-season cooking - frozen fruit and veg.
"Frozen food is not only great it is often better than fresh, especially when you steam it instead of boiling the hell out of it."
"I cut potatoes into cubes and steam them to make mashed potatoes and they are better and it's quicker."
Swapping a green salad with cucumber ($6), cherry tomatoes ($5.49), and iceberg lettuce ($.5.49) with a tasty slaw including cabbage, carrot, broccoli, and a bit of celery would save close to $8.
A mid-winter pavlova is cheaper topped with a couple of in-season kiwifruit at 56c each rather than a punnet of blueberries for $9.99 (if you can find them).
"If you want a salad with cucumber at this time of the year it is going to cost you a lot of money - so pay that or choose something else."
"If you really want to buy produce that is imported and out-of-season you will have to pay extra."
Turnbull said shortages because of the impact of Covid had also pushed prices up or affected the availability and would force shoppers to find alternatives.
"It is not just seasonality anymore. There are transport or staff shortages because of Covid and orchards that can't find staff to pick fruit.
"There is a lot impacting the price so we need to learn to adapt."
Turnbull suggested following New Zealand chefs and cooks to get inspiration that was relevant to New Zealand seasons.
There were also websites such as healthyfood.com that had a filter so you could choose recipes with in-season ingredients.
Turnbull's top tips
Go for seasonal recipes and adapt if you need: Look for recipes that are designed to suit the season. Follow local chefs who will be working with the prices we have to manage in NZ.
Love salads? When cucumber and tomatoes get too pricey, swap to slaw as your base. Use cabbage and carrots as the base and add in other veggies as you like … red onion, celery, finely chopped broccoli all work well!
Frozen is great: Be it fruit or veg, frozen is a great option! Peas and green peas can be a great substitute for courgette. Corn is perfect to make fritters with or add to a winter salad for extra colour and goodness. Frozen fruit is great for smoothies and to add into porridge.
