I recently ordered 4 monitors (1x7" visor mount, 2x5" headrest,
1x7" roof mount with TV tuner and antena), a VCP player,
a DVD player, a 10 Disc DVD/CD changer, plus the FM modulator, Video amplifier/spliter, AC/DC convertor, to outfit my S500 and
a Honda Oddessy. Total cost $1770 for all the components, not
including installation. (btw, can someone suggest a good local
installer in Columbus area ?)

The place I bought those from:

http://www.theautoaccessories.com


They are very reasonable. 5" starts at about $120, 7" about
$320, and they have a good selection. Some places charge twice as much for the same products. For example, Columbus Car Audio wants $1200 and $1800 for the 10" and 13" monitors, the same models from the above site are $699 and $799
respectively, so do a little shoping.
Check Ebay and you will also see a lot of vendors selling these
monitors.

Good luck