Austin with a 10 and 14 yr. old on a budget
 

I have an awesome friend in Dallas who will have a 4 day weekend to spend with her kids (not 4th of July, but in Aug.). She has a tight budget (read $100/day). Her kids are very inquisitive and much more into nature and art than video games and such. They would love to go to a drive-in movie as well. Any suggestions?

See The Bats come out from the bridge(assuming that the bats still do this).

I've never been to the Blue Starlight Mini Urban Drive-in, but this is the only drive-in theatre in Austin. (Actually, I might have to give it a try when I'm in Austin this summer!)
http://www.bluestarlitedrivein.com/

Yes, the bats still come out each evening from the Congress Avenue Bridge and it's very cool. Here's info on that: http://www.batcon.org/index.php/get-...tegory/51.html

If they like nature, they should enjoy the Texas Natural Science Center (Texas Memorial Museum) on the campus of the University of Texas and admission is free.
http://www.utexas.edu/tmm/

The Blanton Museum of Art would be an excellent choice if the kids enjoy art. There's an upcoming exhibit on cats and dogs in art that looks interesting. Admission is $9 for adults, $5 for teens and free for kids aged 12 and under.
http://blantonmuseum.org/

And on a hot Austin day, a swim at Barton Springs Pool in Zilker Park is a must. Parking is $5 on weekends and the cost to swim is $4 for adults and less for the kids.
http://austintexas.gov/department/barton-springs-pool

Great feedback. Anyone have any good ideas for lodging?

I generally stay with family when I'm in Austin, but Jodi123, a Destination Expert for Austin on Trip Advisor, gave the following recommendation to a question about Austin budget hotels in March 2014:

"Often recommended budget hotels are Austin Motel on S. Congress and the Extended Stay America Downtown, both have a lot within walking distance, but the Extended Stay is a straight shot down Guadalupe and closer to the museums (Blanton, Bob Bullock) which are still a good hike or bus ride away. It is in a great location, walking distance to Whole Foods, on 6th St and usually a reasonable rate - http://www.extendedstayamerica.com/h...owntown-6th-st

The Blanton is free on Thursdays and the Bob Bullock Museum is free the first Sunday of the month.