I'll lend a different perspective.
@hindsight2020 just went through the exercise of shopping around for an engine and I don't dispute his numbers at all, but I will say there are multiple techniques for separating a feline from its skin.
I just completed a major overhaul of my O-360 and got the plane back in the air at the end of June. I spent $27k, including removal and reinstallation of the engine. I have four new cylinders, new crankshaft, new camshaft, etc. In fact, the only parts that are refurb'd instead of new are the cases, the conn rods, and the rocker arms.
When hindsight2020 says "
if you're not doing any of the labor," understand that doing much of the labor yourself makes an enormous difference. I did most of the teardown myself, and assisted my A&P-IA with the assembly and installation, but even that's not the end of it.
The amount of time required to research the correct part numbers, ADs, service bulletins, etc. to overhaul a half-century old engine is enormous. It's not made easier by many parts being obsolete under the original p/n and having to wade through lists of this is superseded by that which is superseded by this other number, but it's not available, but such&such is an acceptable alternate, and so on. And that's not just for major components; you'll run into it for washers and seals and bolts and nuts and on and on and on.....
Then there's locating the parts. Who has what in stock? What's the price? Then there's finding shops to do refurb work, and what's their schedule, and OMG I'll have to wait six months to get my crankcase back but these other guys can halve that if I'll pay an expediting fee. And then packing and shipping and insuring.
Doing all that ca-ca yourself, even if you don't spin a wrench personally, unloads a lot of time from your mechanic. Plus your mechanic might not have (or take) the time to shop for the best pricing.
Anyway, my overarching point is that you can bring down the price of an OH significantly by working with a local A&P that you trust and doing a lot of the work yourself. Don't let the fear of a $100k engine job dissuade you if you have the time, skill, and inclination to get some grease on your hands.