If you are going to go into production the easiest are among the many Oyster varieties; they are not as photogenic as domed fungii, yet taste is fine.
You can grow them on waste cardboard - they degrade (eat) lignan, even sawdust. Turn over can be quick & even massive if you scale up.
Most practical initially is to buy their prepared grain spawn & innoculate your fruiting medium.
Oysters waft plenty of spores so find a place other than your favorite room.
Shitake have become very well regarded & you can (again) buy their prepared innoculant. Dowel plugs are practical to stuff into a log & wait around for colonization.
Buttons are what most people have seen. This is not a gourmet mushroom & usually their grow medium entails manure. Commercial buttton growing operations can not be competed with. (If you buy their spent medium as "mushroom compost" be aware it may be ridden with industry chemicals used to control crop contaminants.)
You'll need to pay attention to temperatures when consider seasonal suitability of the different 'shrooms.
Sorry, I do not sell mushroom spawn ( the first stage is desireable strain isolation, then fungii's mycelium proliferation & next transfer of culture to a substrate for mass proliferation of the mushroom "roots", called the spawn ) which you need to put among your bulk growing medium in order to harvest the fruiting bodies.
I don't think the all included "kits" will give you a profit margin.
Be informed that growing a mushroom from it's spores does not guarantee you will replicate it's characteristics.
Aloha Medicinals, among others, has a superior mushroom strain bank. Don't expect any commercial enterprise's mycellium snippets to be cheap , they are proprietary.

You're quite the scholar gringojay, thanks for the overview. What do you think of Stamet's Fungi Perfect? He seems to have excellent technique and rigorous in his approach. I'm wondering if mushroom growing kits would sell at a farmer's market.

Stamets' book(s) are probably what you will be using as guide(s) if you get into edible mushroom production.
I never felt the kits were inexpensive & your mark up might make your inventory turn over slow.

On this subject - I was thinking... I wanted to try growing shiitakes but I have no oak trees to get logs from. Do you think if I contacted tree trimming companies and had them bring chipped oak tree mulch, if I bagged it up would I be able to grow shiitakes? From purchased sawdust spawn, probably. Mind you I've never grown them before, plan on inoculating logs for oyster mushrooms this spring but I was just wondering if that would work for shiitakes.

I sell wild mushrooms at our market, 9-13 varieties depending on the season, fresh and dried. They are very popular.
There is another vender who sells oyster mushrooms he has cultivated, and sells out every weekend.