I wanted to see how much the book is going for, so I took a quick look on Amazon.com
http://www.amazon.com/DIFFERENTIAL-EQUATIONS-using-HP-48G-GX/dp/1886801193/ref=sr_1_fkmr0_1?ie=UTF8&qid=1370269030&sr=8-1-fkmr0&keywords=differential+equations+with+the+hp+48g
and it is on sale between 331 and 900 USD. It seems a lot of money.
Interesting enough, amazon.de lists a seller who sells it for a reasonable 33 EUR
http://www.amazon.de/Differential-Equations-HP-48g-Gx/dp/1886801193/ref=sr_1_fkmr1_1?ie=UTF8&qid=1370269052&sr=8-1-fkmr1&keywords=differential+using+hp+48g
No idea why it's so expensive, anyway I thought I'd share in case somebody is interested in the reasonably priced unit