What are the major differences between a UE or SDT system that costs thousands of dollars and a 2-3 hundred dollar system. Examples of those systems are:

http://www.inficonultrasonicleakdetectors.com/en/whispe...nicleakdetector.html

http://www.reliabilitydirect.com/ultrasoundproducts/ACC-vpe.htm

Here is a broader list:
http://www.reliabilitydirect.com/ultrasoundproducts/leakdetectorindex.htm

The VPE and Whisper are primarily used in HVAC and small manufacturing applications - the SDT/UE are more of a condition monitoring tool with a wide variety of applications and software available.

The environment in which you are working is a major consideration for what you purchase. Another is the applications you are interested in using the ultrasound for. Bearings, Acoustic Lubrication, Electrical Scanning in a lound environment CSI, SDT and UE would be your choice. However, if your environment is confined to a laboratory conditions, say low ambient noise than Accutrak, CTRL, etc... should be your choice. Another of course is flexibility, SDT seems to have the most flexible instrument having such items as db sensor, acoustic lub adaptor, and an RPM sensor all interface with the SDTs datamanager software. Watch this company in the near future. Distance, both UE, CSI, SDT, CTRL and even the Accutrak and Ultrasonic of Florida can hear a 5 psig leak from .050 of an opening of 5 psig at 50 feet. Its when these units are used in the high noise environment that separates the men/women from the boys/girls (PC). No matter whos instrument you are using, get the training you need from a source that has been around the industry. Find a vendor neutral trainer, the less about time devoted to a sales pitch, means time you will have for training.

Our UE2000 unit costed about $7000 in 1999, included a 4 day on-site training conducted by a foreign company specialized in Vibration, Ultrasound etc..

I could have opted for buying the meter only, train myself and look around for someone to join me. Since I also had a lot of other things to do I opted for buying the equipment with training of 10 individuals.
I doubt that someone selling a meter for $300 will offer that service. At the end it will be your equipment and all other people in the plant will say it is your project, and they want nothing do with it.