Gale,
All good advice above. As for the under $100 question. I see you, much like me, are an investigator on a small budget. CHEAP is my specialty!
The Olypus VN6300PC which CP mentioned (thanks CP) is a great very affordable piece of equipment. It can be purchased from Amazon cheaply, or from Radio Shack or Walmart for a bit more if you want it locally.
Adding to that I would get a small external microphone and perhaps a radio shack telephone magnetic pickup for recording EMF audio frequencies.
I would suggest one or more video recorders. I have a tutorial on this site about how to convert a cheap Keychain camera into an Infrared recorder. You can do that for around $40. You can also purchase a low end entry EMF meter for under $30.
Once you have that, the next thing I would save up for is a DVR system. You can also look into some low or no-tech gear such as dowsing rods and pendulum. Although bear in mind that those devices will require a bit more practice and research. And perhaps some time spent with a master to teach you how to properly use them.
Also when you have a bit more money, I would suggest investing in a good high quality camera such as the somewhat older Nikon D70, and IR filter and a good tripod.