Hello and welcome to the forum
WFP system prices vary from about £1,000 for a portable system, to about £10,000 for a van-mounted system.
Whatever system you go for, it wont be cheap (compared to normal WC kit). My advice is to get quotes from as many suppliers as possible.
Have a look at some of the older threads and you will see there are are a fair few reputable suppliers.
-Philip