I've been a seat license owner since before the track opened and have attended every F1 race and many others. I was just at WEC a week ago. I've flown in and out of every airport mentioned and have stayed in San Antonio one year. I would not do that again, even though San Antonio is really nice. It's just too far for getting to the track early and leaving late. And there is a lot of cool stuff going on in Austin that weekend.
If you can fly into IAH outside of rush hour, it really isn't that bad if you don't mind driving. Rush hour though... noooooo. I flew in there and drove to COTA just last week and it was a breeze. But we like driving. Just make sure you avoid toll roads or those savings will be lost with tolls and possible charges from the car rental company.
SAT is definitely the easiest drive. DFW wasn't too bad, but I've made that drive many times and there are always kolaches in the middle to break up the drive.
As for hotels, look at Round Rock. Hotels in Austin are crazy high and are even if you book a year out like I do, but RR can be a bargain. Also some great deals up in the Arboretum area. That's where we normally stay but have done RR a couple of times. Having been to Austin dozens of times, I don't care if I stay downtown but that's just me.
I will likely fly in and out of IAH myself this year. The flight times out of AUS on Sunday night are too early and if I'm going to fly on Monday anyway, why not save a few hundred dollars? For my preferred flights, I think it's about $300 less for each of the two of us to fly out of IAH which is huge.
If price and times work, just fly into AUS. It's a very easy airport. IAH has a rental car shuttle that ads time. But like in our situation, it's a huge savings to spend a little more time.
As for Spirit or Frontier... nope. Won't fly those again. Awful and tons of extra charges.