Cheap mufflers will never give you good sound. It will make your car sound ricey, fart cannon, etc. If you really want to find out what the mufflers sound like, checkout youtube for "mazda 6 mufflers". I like how the magnaflows sound, but I'm not going to put that on my car because my car isn't as fast as it sounds! So, I put on 3.5" tips on the stock mufflers and did the air box mod.
It's truly up to you what you want to do. If your going to do engine upgrades, get the magnaflows. Some say they are loud, others say they are just right. I did the air box mod (free) to see what it would sound like before I dropped the $400+ on a magnaflow setup. I'm happy with how it sounds, but I'm also 25. I don't want a 150hp Mazda 6 sounding like it's 500hp. I'll be buying a muscle car next with at least 300hp...then I'll put loud ass mufflers on it.