When it comes to paranormal investigating it can be a very expensive depending on the equipment you use. EMF, K-2s and Mel Meters can cost a lot of money. So, it is very important to set a budget for yourself as to what you can spend and on what not too.
I will tell you this that it doesn't take much to do a paranormal investigation. All you need is a watch, pen, paper, digital recorder, a small camera (if necessary), permission and daylight. Yes, I said daylight because spirits are active all the time, but more often at night.