I'll second that and add that's I did it once with a donor car. Never
again, not worth the time or money. Not a big modification but still
not worth the grief. I would still own my '72 if it had the automatic
but that's me and probably my age talking.

I think Keislers conversion kit is about $6k auto to 4 spd
Donor car may be hard to find, but 4 speed itself shouldn't be hard to get
A vette salvage yard may help
Expensive would be Ecklers , corvette America etc for all new parts / sans
the tranny
of course you now have an auto set up to recoup some of your expenses too

=============================================
The operative word you used was 'expense.'

Mere mention of finances makes me agree with Bob on this one.  Another,
on the tip of your tongue is probably, 'estimate' -- wrong!  That word
is spelled G-U-E-S-S.

When the 'bolt-ons' & adapter plates fit as advertised, it's nice.  When
they don't you get into welding (very dusty) and machine shop work
(expensive).  Two weeks ago, I had a 13/16" hole machined into an
adapter plate for my floor jack.  -- $ 42. (Six minutes of setup, six
minutes of machine time, five minutes to clean it up & write the work
invoice--lowest priced shop in town.)

In '57 I had a spare car and did a Dynaflow to 4-speed
conversion--wanted a 'sleeper' for street use. (Personality disorder.)
Job turned south when I had it all apart and found that the kits were
made for an 'early' production car and my '54 was at the tail end of the
run. There were no kit pieces for 'late production' cars.  The parts
guys at dealerships found parts that would 'adapt' the car back to fit
the aftermarket stuff.  I did much of the machining in the ships machine
shop.  Close work was farmed out since shipboard lathes aren't level and
cut tapers.  The welding was all farmed out--PJ doesn't weld, PJ burns
holes!  {:-[

When finished, it was a fun car and it worked for me.  The liberal
'guess' of $385 had more than doubled.  Steep for a car worth about
$1600. (Multiply these prices by something between 8 & 12 to get some
guesses.)

If you farm out jobs in a metropolitan area, those jobs turn into a
series of phone calls, parts searches and having your car moved around
the property during work stoppages.  You may have to have the car hauled
cross-town.  The car picks up shop dust and the surfaces get scuffed
from people brushing against the car cover when it's temporarily in the
back lot.  Then, there's the matter of unexpected welding that causes
more dust.

During the work, the words are, "I can't go backward on this.  I'll
spend the extra few bucks to finish the job right," etc.

Or, forget 'expense,' 'finance,' and 'estimate.'  Take the car to a
respected Corvette shop, tell em what you want and sign them a blank check.

Hope this helps.
--
PJ
'89 Hookercar '02 e-blu 6-spd coupe