MM wrote:

Are there any really cheap ones? I need to look inside an enclosed
space.

What's the principle of operation and could one make a simple device?

This came up not long ago, and I saved the following link, which might
be useful/interesting:
http://www.dansdata.com/pencamera.htm

There's a Scandinavian on Ebay who flogs them from time to time:
http://cgi.ebay.co.uk/ETime-Home-Endoscope-USB-Pen-Microscope_W0QQitemZ160204152851QQihZ006QQcategory Z30921QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Try this thread too (started by yours truly) which has some helpful
suggestions too (and no, I still haven't got one myself!)

http://groups.google.co.uk/group/uk.d-i-y/browse_thread/thread/719e100a377e3bac/0b8fa58b352c33eb?lnk=st&q=#0b8fa58b352c33eb

David