Cibula:
Certainly if Roto-Rooter will come back to finish the job free of charge, they're the obvious ones to call. But,...
...my best advice is to keep your old yellow pages phone directory every time you get new phone books for a few years. Any NEW ads for drain clearing plumbers that show up in the new directory (that weren't in last year's directory) are new companies started by people who are confident they've seen it all and learned it all working for someone else that they've taken the leap of faith and gone to the Bank of Dad to borrow the necessary funds to buy their own drain clearing equipment, and are now starting their own drain clearing business.
And, those guys ain't dumb either. They know that their former company was charging you twice what they were getting paid for each job, so they're counting on the fact that they can charge less and still make more than they did as an employee. And, of course, they're hoping that charging less than their former employer will keep them busy and their business growing.
Until you get next year's phone books, just phone around to the companies in the yellow pages who can't afford a full page ad or to advertise on the radio. You'll get just as good results for a lower cost from any of them. But, talk to several to make sure they're not charging as much as the Rooter anyway.
But, I've found that you get the best results from the youngest companies because the work is most often done by the owner of the company, and he knows that the success of his business depends on his doing the best work he can for each customer he gets at a competative price, and so you both benefit. His business grows and gains a good reputation, and you get a good job done at a good price. If you hire a well established company and even if they send their best employee, he knows that he's gonna get paid the same whether he does his regular work or the best job he can. So, what do you think he's gonna do? He simply doesn't have any motivation to do it the best way he can. Only the owner of the business is in that position provided the customer understands the differnce and is willing to pay for any extra time it takes.
And, what I do (which I think helps), is if a new company does a good job for me, I send them a card that they can pin up in their office somewhere (in a blindingly obvious place) saying what a great job they did and to use me as a reference for any other potential customers who may ask for references. That is, you help some young guy out with his business, and he'll reciprocate the favour cuz he'll remember you and help you out as far as he can. For the $3.50 it costs for a nice card and the postage to mail it, it's very cheap way to have a knowledgeable tradesman available you can turn to that you trust will give you honest advice.