I would advise the Round Rock ISD, which is a school district in Round Rock, Texas and northwestern Austin. Some schools in RRISD are located in Austin, while most are in Round Rock. If you are looking for cheap homes and good schools then northwest Austin is your best bet as Lake Travis ISD and Eanes ISD areas are quite expensive. Austin ISD is a good school district, but like I said RRISD is probably your best bet.
hope you have fun in Austin