The last time I heard a discussion on the cost of a new aluminum flathead was about 6 years ago. At that time, the cost was stated to be big...like at least $9K big. About the same as today's cost for a 502 Ram Jet or a World Products small block 427.

I really dig flat heads, but I'd go for one of the other two (or maybe a 5.7 Hemi). I'd prefer a better return on my investment than what the flathead would yield.