That seems a bit high. I just ordered a Soma frame & fork from the LBS for $375 and I have seen them online for as low as about $325. Although I don't think either of those prices included the headset.
Why would you want the Soma frame and the Surly fork?
With the headset, seatpost and stem, that seems like a fair price - as long as the stem and seatpost are what you need (right size, etc). I don't really know how the Surly fork compares to the Soma fork though. I know they are similar prices though.