I heard back from my friend, he reckons you'll be doing well to get it all for £250 (at least if it's all new). The panels will probably go up in price quite a bit, he reckons you'll end up paying about £100 per 100W panel. Also don't forget that unless you can charge the heli batteries direct from the LA batteries you'll need an inverter a decent one of which will set you back a bit.