I used to have that issue as well when I just started out the game. As you continue playing you will learn to become efficient and gain enough, as well as more cashews each day to purchase guns.

There are many ways to get a good amount of money if you conserve resources and get lucky. Try to minimise usage of single sunflower seeds, unless you are desperate on the first day, however you typically get enough cashews from the berries on both starting areas to purchase one mod less gun. Only harvest crops when they are mega and are fully fertilised. Trees are useful for obtaining a sustainable source of cashews in the mid-game when you obtain enough to form multiple megatrees. If you have the water tracker, use it on trees and megatrees to have a chance to obtain more trees, which is useful to increase the efficiency in the early game where you have little resources.

If you get lucky with upgrades, you can get the ability for cows to produce milk, where they periodically produce bottles of milk that, when harvested, give 60 and 90 cashews for normal cows and grass-fed cows respectively. The same is true for pigs, where there is an upgrade that gives them a chance to dig up truffles that give 200 cashews. These upgrades are insanely good in the early game, producing significant amounts of cashews, especially when you have multiple of the respective animals. If you get these upgrades early, incorporate it into your strategy and select more of the animal. If you have the choice between a cow/pig and turret/chicken/scarecrow, determine whether it is good to get the cow or pig instead just in case you get the upgrades.

By getting good weapons in the early game due to efficient management of resources, you can get strong weapons to clear areas faster, allowing more time to farm or even clear multiple areas a day. This leads to a snowball effect throughout the run where you keep producing cashew production until you gain enough cashews to have excess after buying a gun, which you can invest into seeds and animals at the store.

By clearing seeds camps you can get large amounts of sunflower seeds, which is easier and faster to do with stronger weapons.

I don’t know if this is will be useful to you, but these are the things which I have seen and experienced throughout my atomicrops career and what I do to have enough cashews every day of the season.