$6-10K for a crate motor depending on what you load onto it is pretty common. Considering an engine swap for a stock motor used goes for $4-5K, it's not surprising that this is the cost for a blueprinted, loaded semi-race engine with a lot of go fast parts in the right combination. Some shops will even break-in the motor for you and so when your new toy arrives, it is a pure drop in and go to tune affair.
customer service is what will set apart the good from the ugly. considering that Spoon is across the ocean and you are dealing with the less knowledgeable retailer, you have to be careful about what you get in support afterwards locally.
you are paying for someone else's smarts, experience, and knowledge of parts combinations that work as well as a good assembly job...8k for a semi-race engine considering you put zero effort into the research, expereience, planning & building (ok don't rag on me : I meant you worked hard to get the money to pay for it but had no part in the engine building part) to me sounds fair...but I don't have that kind of money. Plus you as an enthusiast gained little from the experience (yes I know, negative experiences are not fun to learn...I've been there). So no hassle and no learning.