I will just say that the advantage of ECR is that they know all the ins/outs of the engine and SPECIFICALLY what to look for and check when assembling engines. But yeah, the $$. If the $$ isn't as big a concern, then definitely.
That all said, building an engine, using your block and pressing in top hat liners and all that is not rocket science and is quite doable. Many of us have done it. A local shop could do it, just need to give them proper direction. The thing is ECR knows exactly what gaskets to use, which sealant makes most sense and will most likely have one in stock and/or get it out to you quickly.
My leaning is ECR if money just isn't that big a concern. If it is, then a shop. If time is no concern, then I would do it myself along with my local machine shop.