1 Year old cat with diarrhea

i just got this cat a week ago so he’s new to me and new food and environment. i noticed diarrhea a day or two ago. I took him to the vet and they quoted me 900 dollars for diagnostics. He’s still eating and drinking water and nothing seems too abnormal so we did then pan luek test and it was negative. I brought him home I want to try some cheaper remedies and see if it improves. Has anyone tried this or thinks it’s a bad idea?