Is it possible? Planting all day sunny plants inside a forest or under trees? I think this can be done, and done very cheap. That of course depends on how large of an area of land the crop will be planted in.
I will keep this article very short just give you the idea with the ingredients. I am going to leave the thinking to your own imagination.
Ingredients; Trees to use as post to mount on, hardware to mount to the trees, 12 or 6 volt light-emitting diodes for illumination, thin copper or aluminum wire to connect to light-emitting diodes, and then one solar panel.
The solar panel does not need to be very big because of the low wattage of the light emitting diodes. But you will need to be able to place it in a sunny sided area of the land.
Nothing else should be needed. If the clouds come out and block the solar cell, it will be no different than if you had planted in open land with no lamps.
The idea is to just charge the light-emitting diodes when the sun is out to give enough light to the plants that are planted under the trees. This is a scenario when full sun plants are desired, but the land has trees on it blocking out the sun. This idea could allow a crop of something like lettuce or even corn be placed inside a forest.
The cost would depend on the market rate, the distance from the solar cell, how many light-emitting diodes will be used based on land area.
The idea is for the light-emitting diodes to run during the sunny part of the day. This adds light under the trees where the sun is blocked. It already has ambient light from the sun, but now added the light from the light-emitting diode to compensate for the shade. This is to give enough light for the plant to grow.
A person should do more research on this subject, and maybe try small expeirements to see if this will work before starting a huge project.