It is extremely inexpensive when compared to commercial reagents. In fact you can prepare 100s of ml of reagent (and store it) for the price it costs for other reagents. We use it routinely and get >95% transfection efficiency in HEK293 cells.
Our protocol is as follows.
Seed cells in 10cm dishes at 4.5E6 cells/dish in 10ml medium (the day before)
Prepare complexes (7ug/DNA, 21ul 1mg/ml PEI) in 1ml serum free medium