Muffler Replacement

I have a 97 Contour GL. I went to a mechanic and asked about a new muffler because mine has a huge hole in it. He told me some times if there stock exhausts then I'de have to go and but a whole new exhaust system just for the muffler. Is this true? If not then is it possible for me to just buy a muffler and replace it myself, is it welded on or clamped?

Don't think you need to put on whole new exhaust system. Even if it's welded it can be cut and have an adapter put on it to install the muffler. My Escort has all stainless steel exhaust. I think the same is true for your Contour. If so how did you get a big hole in the muffler? Go to a national muffler chain. They have mufflers and adapters to fit most any car. Don't spend a small fortune at a garage that will bolt you up a whole new system just because they aren't equipped to just install a muffler. Mufflers are very low tech. Just about anybody with the right tools can replace a muffler. You could do it yourself either way. If it is welded in you can cut it off with a hacksaw and use an adapter. If it is clamped on and you are careful about spreading it with a chisel to get it off you wouldn't have any problem putting one on.
I'd get a second opinion.

Stock muffler is welded on. Like Dave said, any muffler shop should be able to weld you a new one on.