The cost valve could be any where from $15 on up depending on size and such. Patrick is correct about labor. Cost is $180 for the first 1.5 hours and $120 per hour after that.
The first 90 minutes are counted together for a plumber at $180, increasing 30 dollars for every 15 minutes of work, the materials cost would be more easily determined when the plumber sees the issue needing to be fixed, but for a new valve depending on the size the cost would be at least 50-60 for the cost, cant really determine how long the job would take though.
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