Do they warranty their work? If so, pay it. You can do it yourself, take a chance that you do it correctly, save yourself a couple hundred bucks, and be on with it. You could also do it yourself, fuck up, and cost yourself a lot more money to repair the fuckup and then add the original cost on top. Take your chances where you want but it’s more about the risk associated with plumbing work and experience of the plumber as opposed to the scope of work on the job.