Dont forget you ve got a metal cabinet, 2 decent batteries and boxes,smart split charge relay kit and electronic unit,a commercial battery charger,a digital controller with frost stat on top of that.......plus fitting and the extra bits needed to integrate into the fuel sender on top of your vans diesel tank......then theres the fitting and labour costs(drilling through the van floor for the exhaust and vent pipes.etc)..also £750 of the 4.5k I paid was VAT!