The user base would drop ridiculously fast. Imagine if other social network sites charged to be used.

"Nah man, I didn't see your party on Facebook. I forgot to pay my bill on time"

If you want to get started on calculus, check out what textbook the nearest University uses and just go with that. It breaks degeneracies when choosing the book, and you can assume it is as reputable as the school who uses it. It's not a perfect system, but it'll get you going; once you have a book, really getting to know it inside and out is the best way I know of to master a topic. It may seem weird, but many of the graduate students in my program have emotional connections to certain pages in textbooks because of how much time we spend with them.

Once upon a time I did a lab were we used a very simple scintillator and an old photomultiplier tube to detect muons and estimate their lifetime. If you have the parts (including the electronics), it is fun. Exciting? Well depends on the student.