Purchased house for a dollar and I am now selling nine years later.

Hello, after my mother passed 9 years ago, my father sold me their house for one dollar. I am the trustee. The arrangement allows him to live in the house. My father is now a 83 years old and stairs in the home have become very difficult for him to navigate. He has to go upstairs to even get into the home and then go up another flight of stairs. I worry about him being alone in the house and him falling. I have the opportunity to buy the condo next to me, which is on the first floor. My father is in full agreement with me to sell the home so we can pay for this condo that I am purchasing. My question is how much capital gains tax would we have to pay if the home sells for 500,000. Am I taxed for $499,000 since I only purchased the home for one dollar? I live in New Jersey, so I’m sure I’m going to have to pay both federal and state tax. I’m a little overwhelmed, and I don’t understand the process. Thank you so much in advance.