Suns are more expensive due to being more popular for the bright color alone. Quakers can be as friendly as conures, it's not that the bird is a one person species, it's more the gender. If your quaker or conure is male, it can decide one of you is his mate and will be more attached to one person. to counter this, or try to prevent it, you both should give treats and attention equally. Never feed them from your mouth though. I made that mistake once with my roommate's indian ringneck. I still have to watch him a bit when he's interacting with me and reject his advances. See, mates feed one another from the mouth and when your bird tries to feed you, they regurgitate.
Expect a cheaper bird if it is older, expense is mostly due to the novelty of having a chick. Suns, expect $400-$600 for a chick, nandays probably around $400 and under...well, not sure about your area.
They can and will scream for attention and it can take years to train them. Some are just bullheaded and never learn. I live with a screaming sun and have for eight years. My own sun, had him not screaming in a few months, at least not for attention anyway. He was pretty old when I got him though. Older birds are also cheaper because due to lack of experience and lack of proper training or time to do so, they can have all manners of behavioral issues.
Likely best to get a chick.