Parts List with lowest prices i could find on ebay.

Bridge Rectifier, 5 for $0.99. so 20 cents each.
http://www.ebay.com/itm/262136736936

1000uf, 35V capacitor, 2 for $0.99, 50 cents each.
http://www.ebay.com/itm/221982317974

5A Adjustable CC/CV Display Step Down charge Module LED Panel Voltmeter Ammeter for $5.09
http://www.ebay.com/itm/141976484176

Diode Rectifier, 10 for $1.04, about 10 cents each.
http://www.ebay.com/itm/252407596572

Total cost less than $5.89

DISCLAIMER: do not use this charger without a balancer. lithium batteries can explode if charged over 4.2v each.