Why does the bodhisattva guanyin say that her items are expensive for some, but free for others ?

Well, it's all come down to faith. Guanyin has several magical items that could help others
 
Free for some refer to : if that person is willing to opened up and accept bodhisattva's helps, than her items are very easy to get.

But some people's hard are cold and it would be really hard for them to retrieve this item

hope this helps