the new generation LEDs are a great alternative. and until this point, yes LEDs have been a waste of money. but now getting 7-10 bands of spectrum, including the same wavelength that HPS's use to generate the hefty yields. it all comes down to the science of wavelength, and the powering. if you get cheaply made LEDs of a previous generation, youll get crap from it.
the new LEDs are more expensive initially (not by much) if you know where to look. we just bought 6 apollo 20's for less than $700 each. and 1 apollo 20 easily replaces 3-4K of HPS. so not only do you not have to have a separate ventilation for that heat from HID lights that you dont have to buy, you also dont need much in the way of a/c. from 2 13,000 btu a/c units down to 1 6000btu a/c. on top of that i save 65% on electricity because im getting more from less watts, and i dont need all the extra fans and exhaust systems using electricity.
edit:but you can buy smaller units like apollo 8's that replace a 600 watt hps entirely by itself for roughly $400. again just have to know where to look so that you dont find $650-1300 price tags on the same units im talking about