Brotato PS4 & PS5

The best item I found to help with this is "piggy bank". Around level 10, you should have decent enough items/weapons so just keep saving and not spending. The 20% bonus really adds up. As with the other achievements. To make it easier, set things to 25%.

There's 2 main methods for this to be done. The first is the piggy bank what is explained in a different guide so I wont mention it. The method I'm talking uses the Farmer.

Farmer method:
Character: Farmer (reach 200 harvesting to unlock)
Difficulty: any
Weapon: pruner
This method uses the farmers harvesting abilities to get the 3000 materials. The farmer has a 3% harvesting increase after each wave, while also getting +1 harvesting for each consumable while at full health. We pair this up with the pruner that spawns a garden that produces fruit (consumable) every 15 seconds (10 seconds when tier 4).

For upgrades, I went with attack speed, melee damage, armor, doge, hp regen, and damage. Harvesting I picked up whenever it was a good choice however I didn't go out of my way to get them.

You can start saving up whenever you wish but I started saving at wave 15, and I had about 800 harvesting, and got it by round 18. Finished round 20 with 1100 harvesting.

You do not need to pick up the fruit during the wave, at the end they all come to you and you will still get the harvesting for each one.