The plush is pretty rare, I've only seen one at an affordable price and I snatched it up myself.
I think the one on eBay right now is around $200.
There's a pvc statue as well that I believe goes for around the same, it's nice but sort of small. Other than those for figures of Lain herself it is just dolls, the price for those vary a lot. Still missing two of those myself.
I guess there was some garage kits as well but I've only ever seen one go up for sale, and mfc lists it as canceled so who knows.