Unfortunately, Magnaflow doesn't sell Magnapacks by themselves, you have to buy the catback system. Unless you get lucky and find some from an internet classifeds section, you can't buy Magnapack mufflers because they were discontinued. And Partshopper has the Flows for $75 a piece, which is a good price.
Find a local muffler shop. They can ususally get a better price on mufflers than you can and can include the labor as part of the final cost. For example, 2 Flows welded at the shop I go to will set you back $180 (parts and labor)...that's a pretty good deal, and it should take about one hour. If any shop quotes you more than $220, shop around. Plus going the welded route will not only save you money compared to the Catback, but it will give you pretty much the same performance of a catback if you stay N/A on your engine (i.e. no blowers.)