Don't flanges commonly leak?

If so there are quality guys that will do the welding cheap. For example, there is a guy 1 mile from my house that has done 2 custom cat backs for me. I paid him $60 for a single muffler and $100 for a dual exhaust on a later car. (myself bringing the muffler, tips, etc) He'll supply the shop, tubes and labor. He even leaves the car up there for you to inspect it all and make adjustments. I think that's a reasonable cost...