A single-day GA is probably pretty reasonable, 3-day GA is likely around $100-120. In 2019, I paid around $150 for the Haas Experience which was just a 3-day GA ticket with extra access to the Haas section (grassy hill by Turn 19) with a quick autograph session with the drivers & a couple souvenirs.
However, the deposit was a minimum $150 up so you could pick & purchase a seat before the public. If GA & sitting in the grass is okay with you (which it is for basically everywhere but Turn 1), I wouldn't place a deposit; you're likely going to only be given the option of putting your $150 towards the bleachers/grand stands.
I would also advise you start putting in your search for hotels or lodging. All the hotel chains in Austin have either already placed their F1 tax on the October dates, or will when those dates become available. Prepare to shell out $300/night minimum at a main hotel chain. The hotel I stayed at the airport this past weekend was under $200/2 nights; it will run me $800 during Formula 1. If you're willing to travel 45-60 minutes out, you can find much cheaper accommodations.