If you think GLH is expensive at just under $3 per watt you should see some other companies. I think the penetrator series of LED panels only use 1w diodes and they want just over $5 per watt.The expensive LED grow lights from companys like glh are amazing, there 290w led outperforms a 400w hps easily, it produces more dense, potent buds.
That said, the cheapest that is worth it that I've seen would be Blackstar 3w diode panelsthat are sometimes only $1.9-2 per watt. I've seen companies that wanted $4 or more per watt, but they always seem to use 1w diodes and not have the tech that GLH and a few others use which keeps more than 1 LED from going out at a time.