11K only seems ridiculous, but it's not at all when you factor in the associated costs. we already established that it's probably about 6K or so in parts, but then add to that things like: sourcing a suitable block, procuring that cuz i dunno maybe you have to drive somewhere to get it and that's time and gas, then disassembly and cleaning of that so there's more time and money on cleaning supplies, then the machine work so there's time and gas to take it over there and bring it back.
an none of those are fixed costs. if you were doing it yourself, what if you had to make another trip to the machine shop? so there's a day or a half a day off work and your gas to get over there and back-- what's that work out to?
then you have the actual labor for assembly. oh, and don't forget all the lube and sealants you'll need. and new fasteners, cuz you can't be charging that kind of dough and putting tatty old stuff back on. kick down probably $20 for paint too. just in that little prettying it up you've probably got $200 worth of BS, throw some nice valve covers and an air cleaner at it and you're looking at more like 5 bones easy.
if you sit down and do the nitty-gritty maths 11K adds up quickly.
could i build a 350hp 318 for sub 5k? yes.
could i build a 350hp 318 for sub 5K and still buy fancy feast for my boys and put gas in my truck? no, probably not.