Hey Stu,
The convenience of a "turn-key" crate type engine is attractive when your time and working space is limited. The money spent buys you that convenience. I'm sure that you know this, sorry if I am being redundant.
There have been many fast and reliable cars on the road with stock based iron heads but with the release of the new crop of aluminum heads, it makes sense to go aluminum. Better flow, less weight and they are just as reliable as iron.
A guy building engines in his garage usually only pays for parts and machine work since none the assembly costs exist. Sure, you can build it cheaper if YOU build it. I've built several engines, made a few mistakes and learned from them. My 440 based 493 would probably cost me $ $6500 or more in parts plus engine block machine work if I were to build another one today.
If this is a one time deal, you may want to take into account the costs of all the special assembly tools and consumables (thread lockers, assembly lube, shop towels, de-greaser, RTV, hand cleaner, etc) will cost you too.
Aluminum heads are a good upgrade now that they are affordable.
Rebuilding stock iron heads with new valve guides, valves, hardened seats, and other machine work usually costs around 1/2 the cost of new set of aluminum heads.
