I am just finishing up a re-build and modest performance upgrade to a TR250 engine.
Here are the rough costs so far.
Head milled .090, hardened exhaust seats, exhaust valve seals, $450.
New rocker arms, push rods, springs, tappets, and rocker shaft, $435.
Engine cleaned and bored .030", crank polished, $350.
Flywheel surfaced, and new clutch and pressure plate, and TO bearing $370.
Pistons, GP2 cam, rod bearings, main bearings, thrust washers, timing gear and chain set, and gaskets, $960.
Other items like spin on oil filter adapter, bolts, nuts, paint harmonic damper re-built, starter and generator re-build ~$500.
Not yet done is the carburetor and linkage build, and fuel pump kit.
All in all about $4,023 in parts and machining so far, and I did all the disassembly and assembly work.
In the end, I will get some boost in performance for about $500 over a stock build.
Oh, I the original TR6 engine I planned to build needed a crank grind for around $300 and the cam bearings bored and inserts installed for another $500-600 had I chose to do that engine.
I was also fortunate in that I had a near new distributor and oil pump, or the cost for new or re-built would have added to the cost.
For another $600, I could go with triples, then another $400+ for a manifold, but I said to myself, "Self, you are 63 years old so how fast will you really drive this car? Enough is enough.", but I got some.