When I saw the Amount for the Job I was thinking that the shop that did the job did the whole thing from tanking the Block on to removing and installing the Liners.
If the Shop supplied the Liners they would likely charge more than the internet price which used to be $20 something to around $30 each.

The Liners could account for at least $100 of the Cost.

Shops sometimes simply quote the cost of the whole job and do not list the parts separately and if you looked at the Invoice you would think you were looking a only the Labor.
Some Shops also do that so they don't have to deal with the Sales Tax. In CA Labor has no Sales Tax (so far).

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84 300D, 82 Volvo 244Gl Diesel