Current motion capture is done with video cameras and reflective balls that reflect IR light from mulitple sources. The cost of the hardware depends mostly on how large the area is to do the performance. The other consideration is the software that converts the data into something usable. There are mulitple issues with using this technique. The major one is the software conversion does not do as much of the work as one would like.
With the use of accelerometers one eliminates the complicated and inefficient software conversion process. The way the accelerometers will work is first one acquires each position of each accelerometer in 3 dimensional space. Then start recording the data. This data will then be smoothed to a curve. The smoothing process will either use 3 or 5 points on either side to calculate the average. Once the data is smoothed it can be used in any application.