I am looking for slow cha cha songs that can be used for teaching new students. Thank you!

Find a computer with a CD-rom drive.

Install "Winamp"

Configure it to read the CD digitally, or copy your favority (fast) cha track to your hard drive first.

Install a tempo changing plug-in such as "Pacemaker" or "Chronotron"

Use winamp to play the track, with the tempo changer set to the speed you want.

This gives you basically the same capability as a fancy pro-DJ CD player... using $300 worth of computer that you probably already own (you did post a message here after all).