Getting Android Auto in a vehicle that doesn't already have it can be a pricey proposition. Some head units can cost upward of $1,000, and then you have to pay to get them installed. There's a good deal today, though. You can get the JVC KW-M730BT for just $280. That's the lowest price we've seen so far.
This head unit fits in vehicles that have a standard double-DIN dash system. Keep in mind, that's not especially common in new vehicles. The KW-M730BT has a 6.8-inch touchscreen with support for both Android Auto and CarPlay. It also has satellite radio, if you prefer to subscribe to that. There's no CD player or HD radio, though.
This head unit is the runner-up in The Wirecutter's Android Auto/CarPlay guide. It gets points for having a large screen and satellite radio, but the main pick (a Sony unit) has physical buttons that the reviewer liked more than the JVC's all-touch approach. However, that Sony unit is substantially more expensive at $400. The KW-M730BT is in stock at Amazon with Prime shipping.