<p>You could take MPGU 120a Beginning Pop/Rock guitar. [MPGU</a> | USC Schedule of Classes](<a href=“http://web-app.usc.edu/soc/20103/mpgu.html]MPGU”>302 Found) It is 2 units, and as long as you don’t exceed 18 units total you don’t have to pay extra. The basics will be the same so you could take a few semesters (120a, b, c) and then move on to private lessons to focus on blues.
As a parent who has (willingly) paid for decades of private music lessons, please let me know if you find a way to get quality private music instruction for free (I have not). USC has MPGU 300x Non-Major Individual Instruction (Guitar), and if you fit it into the 18 units there won’t be an extra tuition fee, but there will be the private lesson fee of $350/semester for 1 unit and $750/semester for 2 units. </p>
<p>You may be able to find students offering beginning lessons, but they will expect to be paid for their efforts. The most economical plan would be to take the three semesters of beginning guitar and then consider private lessons. Good luck!</p>