Even if you cant get a complete 4" for that. You can get a 4" catback for very close to that. Then later on get the down pipe, remove the cat, etc. Eventually end up with a complete 4". A little more expensive than doing it all at once, but works.
My experience, the 4" muffler and tail pipe does not sound much louder that sock, if your are worried about sound. Didnt help that much on EGT's. The sound and EGT improvement came when going Katless. That was very noticable. Still using the stock 3" downpipe.