What kind of market are you in? Near an urban center (where people might pay a premium for fruit and some vegetables) or far away (in which case transport costs might make value-added crops like maple syrup / dried foods / etc. more cost-effective)? Are there products that are in demand but not supplied locally now?
Top dollar for space used would likely be obtained by growing prohibited crops.
As a general rule, crops that are highly labor intensive and highly perishable bring the best prices. So things like berries. Crops that are easy to grow, harvest, and transport to market bring lower prices, because so many people are willing to grow them and do the work.
At my place, the furthest out zones are most useful for growing things that are typically wildcrafted: medicinal herbs, wildflower seeds, bean poles.
Considering the price of gourmet mushrooms and fresh herbs at the grocery or market, I'm considering growing both for market when I retire. Basil,rosemary,lavender,thyme,cilantro,and parsley .
Bamboo is another,if you are creative and crafty. You can make a million things out of it and prices are ridiculous for simple crafts like deer scaring fountains and little flower vases. Plus,the shoots are edible and delicious.
Fruit, especially berries bring high prices but getting fruit grown that doesn't have bug issues and looks good for market would be a much bigger challenge.
If you live in an area where you are allowed to make things for market,
You can make things like pasta or pickles and jams. Nuts bring a very high price. That greatly increases prices but you may need a certified kitchen or other licenses in some states.
Root "spices" such as turmeric and ginger can also bring a high price but you need to be in a good climate for them or grow in a greenhouse.
Have you checked out the "Urban Farmer" videos by Curtis Stone? He's up in a cold Canadian climate,don't remember exactly where.
I've been looking at this stuff for awhile since I will do something when I retire in a few years. I may also consider doing some goat cheese and selling heirloom birds such as turkeys and ducks ready to eat for holidays.
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Getting ready for the Better World Book kickstarter - February 2019