Here we have a bit of a problem...this is a fairly complex project, even for someone with a decent understanding of electronics design and construction... that a person with ZERO understanding of electronics wishes to try.
Im NEVER against anyone trying to learn electronics...but lets be honest, this is soooo far over the ops head, that he doesnt stand a hope in hell of making anything this complicated...even if someone provided a full schematic and circuit description.
lets be honest, changing a calculator over to generate tones for each individual numerical character, then adapting another calculator to decode these many, many tones into a display is a HUGE undertaking.
The average inexpensive eveyday calculator cant even be hacked... its simply a circuit board with a COB covered with a blob of epoxy.
Does the average inexpensive walkie talkie even have the audio range to accuratly reproduce the tones being sent. Every one that I have used had really crappy audio reproduction.
If this book was written a few years later, Im certain the author simply would have had his charaters using cell phones with text, and only devised this silly calculator conversion idea, because no technology existed at the time that would do this.
I know Im gonna be pissed all over for killing a newbies dream...but maybe he should start with how a transistor works, or how to use it in a circuit...or even what its denotation in a schematic is, before taking on such a huge project.
As well, remember that the OP has also specified that he is willing to shell out all of $45 to $50.00 for each unit....making this a bit difficult as well.
And, as far as someone being a Racist......reading a book about Racism doesnt automatically turn someone into a Racist...Ive read Mein Kampf, and Im not a Natzi.