I put about $4200 into mine, doing the labor myself. I did a lot of research before hand and got quite a few bits of advice here before making any decisions. I also didn't buy a kit but bought piece meal of parts I thought to be the best bang for the buck based on reviews.
In that, I did the following replacement/services...
Oil cooler housing gasket kit
Blue spring upgrade
6.7 banjo bolts
Coolant change to Cat
All associated gaskets
Oil change to Rotella T-6
Motorcraft oil filter
Motorcraft fuel filters
Restore/Restore+ coolant flush
Oil rail ball tubes and O-rings
The truck had already had an EGR
cooler delete kit installed
I have just recently found that I had an HPOP
shaft seal blow out and have just put another $1200 (Including shipping) into it for..
rebuild (Stage 1 21* upgrade-Pat, the Diesel Guru, at Diesel Speed and Marine in TX)
rebuild (Included in the $575 price of HPOP
o-ring kit (Because, why not?)
I will be doing another air test, oil change and coolant flush BEFORE the truck gets cranked on again.
Once the cash storm settles I will most likely send the FICM
in for an Atlas 40 tune and 58volt upgrade.
All in all, its been a battle but that's mainly been due to cash flow issues. Ya know, bills over toys....I think Im somewhere in the range of around $6k total with the small extras needed...IE lubricants, additives and the like.
Hope this helps.