I've done several engines myself now...I honestly think I take a lot more time to research, pick parts, measure (with correct tools, not dental floss), and assemble than a machine shop that has a quantity of engines to put out per day. I took the time to weigh and calculate my bobweight to have my 428FE balanced. When the machinist tried to balance the rotating assembly with 100g more weight than what should have been, I was there to know that something wasn't right. Turned out, he had forgotten to zero the scale.
There's nothing hard about assembling an engine....just take your time and be patient.
You'll save money and gain lots of experience!