Great cheaper alternative are VOCOlinc smart bulbs (on Amazon). $20 per bulb and don't need a hub. Only thing it's missing compared to the hue seems to be the syncing to music and movies, but for the savings I'm fine with that ¯\_(ツ)_/¯
VOCOlinc L1 is indeed a cheaper alternative. I haven't seen a HomeKit-compatible smart bulb with full colour range that costs as low as $20. I'm not sure about the 'great' part, though. It's quite dimmer and has narrower colour temperature range than the competition.
Name / Power / Brightness / Temperature / Colour Range / Beam Angle / Price
VOCOlinc L1: 6W, 470lm, 2400K-5300K, 16mil colours, 200° beam, $20
Hue White Ambiance: 10.5W, 800lm, 2200K-6500K, 50k shades of white, 160° beam, $30
Hue Color Ambiance: 9.5W, 806lm, 2000K-6500K, 16mil colours, 160° beam, $50
LIFX Mini Day & Dusk: 9W, 800lm, 1500K-4000K, shades of white, 250° beam, $30
LIFX Mini Color: 9W, 800lm, 2500K-9000K, 16mil colours, 250° beam, $45
LIFX Color: 11W, 1100lm, 2500K-9000K, 16mil colours, 135° beam, $60
470lm is what's normally referred to as "40W equivalent", while 800lm is 60W equivalent and 1100lm is 75W equivalent. I'm hoping that VOCOlinc gets a brighter bulb out in the future that doesn't cost much more.