8mm (Double-8mm or Single 8mm) cameras
Most were made between 1945 and 1960. If the camera is made a metal and really heavy, it's early. If it's plastic, made in Japan, it's later.
These cameras are, for the most part, worth around $5 to $10. There are a few models that are worth more, some considerably more, but for the most part, the Bell and Howell, Revere, Kodak, and Keystone cameras are not valuable.
If you want a more accurate estimate, go to www.ebay.com and look at the completed auctions.
While it is possible to use these cameras, unless you're into lessons in frustration or a technophile, it's not worth the trouble.
Super-8mm cameras, 16mm cameras, and others
The range of prices for cameras is so wide that the only way to establish an accurate estimate is to search ebay.com.
Usability of individual cameras is dependent on condition, something that cannot be judged over the Internet. Cameras should be checked by a competent technician before use. Film is available at pro camera stores and directly from Kodak.
Finally, the best resource for information on old cameras of all types is McKeown's Guide to Antique and Classic Cameras, (also available from amazon.com).
I wish you luck!