http://www.batteryspace.com/exlighthi-powerledbikelightwithbuiltinpolymer-li-ionbattery37v32ahsmartcharger.aspx

$50 for light, battery , charger and mount.
Ok so nots a P7 , but its not $80 .
On paper it looks like a reasonable deal and maybe good for the commuters rather than in the woods at night with the monsters / doggers.
At £32 each a pair would not be an expensive set up , or pair it with a P7 torch on your lid