Isn't overhaul on a Merlin pushing 100K or more now? I know Props are in that ballpark too.
An overhaul is very expensive these days. Parts are getting harder and harder to find. While Rousch is making some stuff, it is a very expensive and time consuming process to get the FAA/PMA stamp. That in turn pushes up the costs of the parts. Another thing most people do not realize is the cost to build forgings and other unique items. While technology has become more available, tooling up to make forged parts in VERY expensive. These costs likely would push the final cost of a new build aircraft in excess of an existing airframe.
'bout 110-125k on the kind side last I heard. You can maybe get it entirely (top/banks and bottom) done still for that but only if you (can (and I mean the shop quoting you trusts youre capable at doing this and thus ultimatley making their job/life/costs gentler)) do most the work for the engine shop of striping it from the cowl and accesories and after it comes back from them and the test stand of reinstalling/connecting/timing/cowling it back in the airplane. Otherwise if your'e looking at the complete drop off and pickup service, and also know it's better to spend more on any wear and tear now than damage later with these things, expect the work done on schedule, etc. etc., I wouldn't flinch at 150k today all said and done (right).
Most of the money is all in the top half, the banks primarily, each half (6) requiring over 120 gaskets, seals and o-rings to be replaced by hand. Four vavles x 12 is also a lot of parts and seats to keep prime (and again, to do right on an old ac engine, reseating all/most maybe = necessary $$$$). And don't forget to think twice about those magnesium valve covers before jumping in to save
a little[/i cost with pitching in with your own wrench.
Authentic/accurate P-51 props, yes... of pretty good static quality and maybe with or w/o the nose cap or hub. With all their airworthiness slips, last I looked your'e looking at about at or just under that price these days, per blade.
For reasons Bodhi pointed out, working on a mustang with a packard merlin (an awesome honor/opportunity assuming you're mortal like me and can't afford one out of pocket yourself (yet)) is like anticipating a heart attack or stroke without health insurance. Parts just keep going up in price (ie: gear doors

)
The shop that does most our museums V-12 work is probabley the best in the world, last time they came out to help us on our SpitXIV retorque he was talking about a DB601 from europe they were getting finished tooling up for overhauling and a DB605 that just showed up also from europe in a crate, to be used in a 109 restoration. While they're doing the 601 they'll microscope and anylise the 605 (infamous for factory labor sabotage), if it pans out then they'll begin tooling (retooling) and overhauling it back to working condition after the 601 is finished. They're probabley working on the 601 right now, but these are not rush jobs so probabley slowly.