I am 95% complete with the same swap into my 72.
My running tally is somewhere close to $4000

I went a little over board on my fuel system and did ceramic headers. Im sure you can do it for less than $3,000. I modded my stock harness too so that was free.

-45,000 mile complete 5.3/4L60e pullout with harness and pcm $1,680. (local Pickup)
-Fuel system(Aeromotive pump and all SS braided lines, an fittings, filters ect.) $700
-Dyno tune $450
-Doug Thorley Ceramics $600
-Early Classic motor mounts $230
-Drive shaft shorten $100
count on a couple hundred for misc. stuff new O2s are a good idea