Fot the ones in-stock you could watch some video review. The price/quality ratio will probably be different for each piece so it is hard to say. For example, with Gaming Heads, the Nightigale was correct, the keeper statue had an awfull paint job but the breton and Kratos on throne were amazing. That said I heard that sideshow make some really great stuff, but it is not always up to the prototype quality.
With Prime 1 (the harley quinn statue) I think you get pretty much what you pay for, prototype = final product.
Before buying, just make sure that it is a character that your really like. Don't buy something just because it is cool. Buy it because you love the character, his story, his personnality.
If you buy something just because it is cool, well, it will be cool the first days after you receive it, but then you will loose interest in it.
And display is also very important. Great light can make your statue look even better. So if you buy one of these, make sure you highlight it well in your collection. I know I am not the best example with my messy display (

too much stuff and no more space) but these are my little advices
And my review of the Destiny Bambaland hunter