Well first i will tell you what i have. I had the same dual inlet muffler on my 97 z71. I had it removed and from there I ran 2 1/2" duals out the back through 4"x18" tips. I get comments all the time on how it sounds and it is extremely loud and deep which is what i was looking for at the time. I would recomend this instead of glasspacks. It still will cackle nicely if that is what you want. However if I was going to do it again i would use a balance pipe, i hear it will make the sound a little smoother and it is supposed to give you the most power from dual exhaust.
About the cheap mufflers, go to ebay and you can get new flowmasters for a good price. Hope i helped.