Money making guide
I have found the hourly profit for each income source and sorted them below. This may not be fully accurate so please comment if there's anything wrong.
For each, the total profit is the income received by a player, minus any costs such as weed seeds for example.
Printers:
Assuming printers are fully charged, cooled, and upgraded; printers can be one of the best ways of making money.
Per hour without an extra printer you can expect to earn £529,000, but with an extra printer you can expect £616,400. Without VIP and a gang, you can expect £266,800 per hour.
Mining:
Because mining is skill level based, I have found the expected earnings from three different levels, 10, 6, and 0.
These are per hour, and level 10 mining earns the most money out of all methods that I have checked - nearly £1,500,000 in just 1 hour!
A benefit of mining is that it is legal, however underground mutants may kill you, making mining sometimes difficult.
Weed:
Assuming you are lucky and are not arrested selling, weed becomes a very good method of earning money when you have more than the standard 2 pots.
The standard 2 pots will earn you £228,000, which means for a solo player, weed is the best option out of weed, moonshine, and meth; in terms of profit, however it comes with the greatest risk.
Moonshine:
Moonshine is one of the least risky methods of making money as it does not require you to travel to an NPC where you could be arrested; however it is far less profitable.
At only £120,000 profit per hour (without borrowing other player's brewers), moonshine is not that good.
Meth:
Meth is a relatively fun and active way to make money, and is less risky than weed as it is far quicker to sell. However, it is not as profitable.
Using a second stove to double the speed of meth cooking can net a decent profit of £430,000, but requires you to be very busy creating the required ingredients.
Bitcoin:
Bitcoin requires lots of set up costs, so takes a long time to become profitable (~2 hours). I have not fully checked the profits of bitcoin yet, but will add to this section later. With a full rack, you can expect profits roughly around £500,000 per hour.
Conclusion:
Max-level mining is the most profitable method of earning money, however it does require a large initial cost to level up. When coupled with printing, you could expect profits of around £2,000,000 per hour!