I have my eye on an antique muzzle loader (early 18th century reworked early-mid 19th century-pre 1850).  What gives me pause though is that the lock mechanism is missing, all other parts are present but the lock work and plate is completely absent.  How much would it cost to have a new one made and fitted?  It needs to be made as a drop in replacement as if I get this I will not tolerate modifications to the stock or any other parts.  I will also need engraving and inlay work done so that the new parts match the work done on the old.  There is no nipple, just a hole so it appears it was still in flintlock configuration, I would like to keep it that way.  About how much would this work run me, and who could do it?

Maker is unknown, but the original barrel Has a crown v proof.

The location of the hole in the barrel is not a true indication of whether the rifle was originally a flint
or a percussion. The caplock came about after the flint, & almost all of the caplocks were designed
to work in original flint rifles. If you find the right guy, about $300.00 might cover parts & labor for
your lock of choice & fitting, with no modifications to the stock. Custom engraving on the new lock
of whichever type you choose can add a lot to that estimate.

The barrel is 18th century so it was almost certainly a flintlock (I'm assuming a wheel lock, matchlock, or snaphaunce was unlikely) I just meant that no modifications are apparent that would prevent it from still being a flintlock.

Any suggestions on where to check for a smith?

Any rough guesses what engraving and inlay might run, or know anyone who specializes in it?

Try this forum:
http://americanlongrifles.org/forum/index.php

There are a lot of guys there that do what you are requesting, repairing original guns, fitting new locks, engraving and most do all three.

I have a friend locally who has fitted antiques with new locks when they were absent and I have inspected the results.  It does work but takes care to find the right lock and fit it without altering the gun more than necessary, and to apply the proper finish to the external lock parts. The cost will generally depend on the condition of the gun and how much fitting is required. Cost of the actual lock will depend on the lock needed.  Check that forum I listed above, post your question in the subforum Antique Gun Collecting or Gun Building.
Good luck

What kind of inlay are you thinking of?  You said No mod to the stock....  You can get Siler locks with blank lock plates that could be fitted to match your lock inlet.

Maybe one of these will work.  Worst case, as noted above, and you'll find them on this linked page, there are "blank" locks that are just rectangular in shape, meant for fitting to an existing inlet.

lots of locks

Gold (or possibly brass, I'm not sure).  The original has lots of inlaid scrollwork on the barrel, I assume the lock was the same way,

Oh I see...well post pics up already!

I'd love to but I don't own it yet.  I'm trying to gauge how viable restoring this is against my budget before I buy it, or not.

Jim Chambers has a flintlock kit that is assembled by you.  You can cut the lockplate (flat rectangular bar) to mate with the missing lock.