thousands - it depends what kind you get. Check the forum sticky...
You will want mics that connect using a 1/8" mic-in jack. Audio Technica and RODE would be in the ball-park. The ZR800 does not have an accessory shoe, so a $10 camera bracket will cove that - again, check the Camcorder forum sticky.
If what you are recording has "normal" levels of noise... background TV, some crowd noise, etc, you will not have the problems with the mics picking up the tape transport. Also, be advised that if the audio is too loud (like an amplified band or you are really close to a marching band), the audio will sound really muddy and cannot be fixed - none of the camcorders on your list have manual audio level control.