We live in an area that both local universities have Super Saturday or the like programs. The programs are $80-100 for a little over 1 month of class. I really want DD to participate but this is pretty costly for an every 4 weeks or so activity. DD is in STEM club at school but we were disappointed to find out it meets once a month.

What other programs or extra activities have your LO's enjoyed that touched on subjects like these do and gave the social aspect too?

I'd also issue a caution about such programs-- do some digging.

Often they are "housed" within a STEM department affiliated with a local university, all right, but the people actually RUNNING the programs are Education department (or not even that), and the ones in classes with students may even be undergraduate work-study types.

So investigate carefully. Our local one has a wide range of what I'd call genuinely meaningful educational activities. Some of them were great (Lego Robotics, Programming classes), and others were totally lame (Science Camp for girls) but at least in the latter case, my DD met another HG student, so it wasn't a complete waste-- she is still friends with her 5 years later.

Chess clubs can be a great outlet-- you may even get lucky and find that such a thing is all-ages and free.

Our parks department has some pretty interesting offerings at WAY lower cost-- including a parent-and-youth balsa glider/model airplane class. My DH and DD took that one together and REALLY had a blast with the physics concepts.