There is currently a cheat/bug/exploit where if you set your name to be certain characters, then whenever your name is said you will receive items. You could potentially earn over 300 million in one day, and tackle the JoJa achievement at the same time. I do recommend doing this on a completely separate save though (your "JoJa save" as it's incredibly game breaking.
This video demonstrates what you need to do - it is not my video.
In case the video gets pulled, start a new save, set your name to be 
. The rest doesn't matter. You can use other numbers to get different items but there's just no point as your name isn't changeable in game.
Once you've started, head over to the Saloon and wait for it to open at 12:00, then enter and speak to Gus. After he says hi, immediately speak to him again.
Upon doing so, a large fish and a treasure chest - the two most valuable sellable items in the game at 5000G each, will suddenly appear in your inventory. Keep pressing A to spawn more (the video shows 1 spawn after each button press + Gus speaking to you each time, but for me I just received 4 per button press). You can fill up your inventory completely with three sets of 999 of each item, take it back to the chest in your house where you sell stuff, then head to bed to sleep. You will then receive enough money to get the 1 mil and 10 mil achievement, which in turn will give you enough money to buy everything in JoJa and get that out the way. Repeat visits are completely unnecessary as you'll have enough anything to buy literally everything multiple times over.
This may be patched in the future (to which I'll try to remember to remove this guide).