This has been beat around many times and the answer in the end is this :
The cost will be debateable based on weither you get it in a coop or just order the parts yourself but in the long run the amount difference would be very small and nothing compared to the cost of extenstion cords lights ect.
The express is a newer more capable system by far.
The express is much less work as you have less to build over all.
You are 10 times more likely to get the express on a coop than the freestyle since I rarely get request for Freestyle pcbs anymore but am always running out of Express pcb's.
The support on the Express is better because thousands have been done so the users know them well.
Hope this helps I do not like to play favorites with my kids but the facts are the facts.
RJ