yep ^^^ what matu said ^^^
tinctures, teas, blends, rubs, salves.
and also common culinary herbs can be powerful healers, oregano tops that on my list. common as a penny though, but a powerful healer.
theres a trendiness to getting rare and unusual herbs, if anything i would rather counter that with simpler more accessible things, but as for your question- growing the rarer ones might be better for money. or maybe not, and the most common and recognizable are what would sell.
i am working on similar things, i have been studying herbalism for a long time though.
i am starting some camellia (tea - green tea/black tea) and i have a ton of herbs growing.
you can grow camellia in zone 7 (8?) down south.
even if it all flops- herbs are great to grow anyway, they just keep getting denser and more and more each year, very easily, with less fussing over than most plants. it is totally worth it to grow lots of them, even if you dont end up selling them.
i am fond of spilanthes - the toothache plant. it has other uses besides just teeth, it's anti bacterial, anti fungal. its a bit more difficult to grow than most herbs, its a tender
perennial but is very sensitive to cold, so tends to be an annual.
herbalism is a huge subject! it can get pretty overwhelming. i think the best way to learn is to take it one plant at a time.
find one you really like and get to know it very well, grow it out, see how to use it...well i suppose one at a time might be extreme, but basically it may be better to know lots about a few important medicine plants that work for you, rather than some general generic knowledge on a lot of plants, that may or may not work as well as suggested, or that you dont hardly know what to do with.
common tea herbs seems like a good place to start --- heres some ---chamomile, mints, anise hyssop /giant hyssop/agastache, lemon balm,
rose, red clover flowers, you could probably grow roselle as an annual or
greenhouse, also raspberry, and blackberry leaves are a good base for an herbal tea. something new i have been trying is tulsi (aka holy basil), i am really enjoying tulsi as a tea herb, interesting flavor with a bit of
honey.
you may also have good luck with selling herb starts in pots, live plants. common culinary herbs like oregano, thyme, sage, as well as whatever medicinal herbs you start growing. because herbs are so easy to grow, and prolific, usually you can propagate tons of starts from an existing patch.