Summer Hull, the author of the MommyPoints blog, had a nice post recently telling how you can avoid the checked-bag and carryon-bag fees charged by Spirit Airlines, simply by reducing down to an 18x14x8 inch personal item. Such a personal item is free on Spirit Airlines.
If your carryon bag is larger, the extra fee is $35 to $65, so the savings that you receive by taking only a personal item are substantial.
Spirit Airlines does not fly to Austin, but you may use it by driving or flying to an airport where they do fly, like Dallas DFW or Houston IAH.
One tip that Summer does not mention is to pack as much as you can on your person. You can stuff your pockets with bulky items. To take it a bit further, invest in a ScotteVest (or an inexpensive fishing vest), which has tons of pockets. You may look like the Michelin Man entering the aircraft, but I’ve never heard of a passenger being denied boarding for that reason.
UPDATE: This blog post reports on a man kicked off a flight for wearing too much clothing. He wore 8+ sets of clothing, in order to avoid paying a luggage fee.