You may be able to get away with 1 7/8 primaries on same style headers. They usally sell them a little larger than what is listed in the catalog. Just make sure your first bend is mandrel bent 3 inch then reduce will help alot with budget exhuast. Not sure how good what you have already. But you can see what i mean about the bend after the header being a large diameter to allow for good flow.
I love the look of side pipes but damn there are times when they sound bad. You have to drive with both windows down or the car sounds aweful. Unless they are quiet and balanced with cross over. Its better to have full on exhuast. Flowmaster probably makes a kit that is bolt on and will make almost as much power as open headers. Also a parts list to this kit may reveal that you only need a few custom pipes and the rest can be off the shelf pipe. But not sure about c3.
Also for 600 bucks a local muffler shop may build you a full 3" exhuast welded on and ready to last a ruff winter. Once you get to that amount of cash some shops wont let you walk out the door some will tell you 1500 just got to shop around.