Drive ins are often old and run down but that’s a lot of the fun! Make sure you bring a truck or a big SUV (cars just aren’t as fun) and a lot of pillow/blankets. You can buy pizza or food and drinks elsewhere and bring it in to avoid using the snackbar (expensive, too). These are the cheapest movies around!
Planetariums range in coolness. Some have sweet star and laser shows, others are just boring unless you’re really an astronomer. I suggest looking in to it though — Most colleges/universities have some sort of planetarium and reasonable prices.