The problem of expense comes into play in a few different ways, but the most significant was in error corrections, where you couldn't simply change out a letter or two. You'd have to recreate the entire line from scratch in the best of cases. In the worst cases, your correction affects spacing enough that the change affects other lines, and you have to recreate several lines from scratch, all for what might simply be the insertion of an extra space.
Anyway, I've come across a discussion of the Merganthaler Linotype machine in Hearings Before Subcommittee of House Committee of Appropriations (for an 1898 appropriations bill), which covers both the expense of errors and and the problems with quality.
Statement of Mr. Th. E. Benedict, Public Printer
The Chairman. Let me ask you. If you avail yourself of modern methods of composition, take for instance, the Merganthaler process?
Mr. Benedict. I can say this: I believe that the working force of the office, if the question were put to them, would say the present Public Printer has largerly added labor-saving machinery to the Goverment Printing Office.
Mr. Sayers. You have not gone to the full length that private institutions have done in the matter of labor saving machinery, have you?
Mr. Benedict. I have gone to the length I was able. I have not been remiss in putting improved machines in the Government Printing Office which I thought would be useful and to the limit funds for such were available.
Mr. Sayers. I am not saying you have not done your full duty, but I am simply comparing the conditions of the Printing Office with private institutions?
Mr. Benedict. If it was a question as to whether the Merganthaler or Linotype was profitable to be used in the Government Printing Office, I have an opinion; but perhaps you do not care anything about that.
Mr. Stone. Do you use any of these machines?
Mr. Benedict. No; but I am very familiar with the machines. I know there is a great humbug about the matter of profit of these machines as operated generally. You need not put this down—I know the conditions under which they can be made profitable, and I know the conditions in many offices where they are unprofitable, and those are the conditions which would operate in the Government Printing Offices. Outside of the Congressional Record we receive scarcely any copy which, when in type pages, is ready for the press. Our page proofs are edited and reedited by you and other editors, and we reset the matter again, and when you have to reset a whole line or a page to correct an error of a letter or a word of the compositor or author, the work is very expensive, and such corrections with the Linotype machine are necessary, as it sets type on a slug, and to take one letter out you have to set every letter of the slug line, and to insert a long word or a few words you have to run over the whole sentence.
If you have perfect copy, the Linotype machine is profitable, and if you do not have good copy it is not. Under these conditions the typographic appearance of every daily newspaper in the country where such machines are used has been so lowered that they have ceased to be respected by persons of taste, and the typographical errors and lack of typographical taste are due to the use of the Linotype machine.
Mr. Sayers. Of course you could not use that for the Printing Office of the Government?
Mr. Benedict. I guarantee that in the average daily newspaper set by the Linotype machine you find from 10 to 20 errors to every one you find in the Record, and you would lose almost entirely the typographical style which makes the Record the most beautiful and perfect daily publicaion of the world, while produced under greater difficulties than are known in other daily offices.
Tell us how you really feel Mr. Benedict.
Granted this is just one point of view, it's still an interesting insider's view of the Linotype and its real world issues. There are plenty of sources out there that more clearly describe the problems with the Linotype (in particular the rivers) as well as the cost of error correction. I just liked this source for its directness.