Wow this brings back some memories! My first computer was also a TI 99/4A. I got mine brand new in 1982 through a friend that worked at TI. For a while I suffered through the slowness of using a tape recorder for storage but eventually I bought the expansion box for it which added memory and a 160K, single-sided, 5.25" floppy disk. Compared to the tape drive it was a speed demon!
Ahhhh .. the "good old days" of buying a computer magazine with programs listed in Basic and typing them all in. Sometimes having to figure out how to convert them because the version of Basic wasn't the same one. I don't have the 99/4A anymore but I do still have a book that I bought back then to experiment with called, "Projects in Machine Intelligence for Your Home Computer".