From memory the first rebuild was about $10k with new JE forgies, Eagle rods, Poncams. ACL race bearings, ARP headstud kit, full head service etc...
Out/In cost $2800 extra plus consumables like all fluids, sparkplugs and gaskets to bolt the boltons back on. Same shop Nik used.
So $12k to $15k is on par with ESP's quote but thats with all NEW pistons, rods, cams, bearings so you should come out if most of your internals are ok for $7k plus out/in of your block.
Second rebuild would have been the same except I needed new turbs, new JE Pistons oversized and I also decided to go more the full monty with 9.5l sump, Nitto oil pump & crank collar, Koyorad, CAB, 2L custom oil catch can, Haltech platinum pro ecu and the list goes on and on. This one is In the vicinity of just over $20k - CRD
Oil starvation twice with big end bearing failures scared the bejeezus out of me.
Now I have more oil than Texas in the GTR