Is $3,500 to mud, finish, and paint a 1300 sqft 2-car garage a fair price?

I found some workers on Facebook who quoted me $3500 for the job. I agreed to the price, but we had a payment disagreement. They initially wanted half upfront, but I proposed paying for the drywall myself, giving them $1000 after hanging it, and the rest at the end. They agreed, but on the second day, they asked for more money, and I gave them $700. I'm concerned they will keep asking for money daily, depleting the job price before completion. I'm trying to determine if $3500 is a fair price for this work, which also includes painting two colors.