The most comfortable boot in the world is the one that fits you the best. If you buy a boot that is marketed as being ultra comfy but it doesn't fit you, then you will be in a world of hurt.
The best advice you can get is to go to a boot-fitter, have him assess your foot shape & ankle flexibilty and try on boots that he recommends based on your subjective biomechanical needs. You should also get supportive footbeds, despite your asking for the cheapest solution. If you do this, you will get a boot that is comfortable, supportive, and skis well. If you buy solely based on brand or what others think is a good boot, then you will not be happy.
WE ARE SKIING.