I don't see the big deal about building something yourself. I do my own motors. I pay for the machining, have it machined to fit the pistons I have, balance the rotating assembly, and put my engine on an engine stand and do it myself once it is all spec'd out from the machine shop. Although I have never built an FS, I have many 4g63s that have made stupid power.....more than any FS I have seen and I have built some high reving B series years ago. If I had the tools I would do my own machining as well.
I am a die hard DIY'er though and I have spent money on replacing things I broke, but in the end I can say that I built the motor. All you need is the know how, a good machine shop, a great and reputable set of in-lb/ftlb torque wrenches. I rebuilt my first motor when I was a teenager and have never looked back.
But if you have the money and don't have alot of time, then get the motor built by a good shop and don't look back.
If you decide to build it yourself, take the time to do all the research you can on "how-to" properly build a motor. Have a plan, take pictures, check and recheck.....then check and recheck again. There is nothing like starting a motor that you put together, and having it run like a top.