On the subject of used parts, the cobb stage 2 paced for my 03 wrx new is $1750(I believe) I have found a few used catted turbo backs on here for $650-900. The access port you might as well buy new. They are $595 new if you buy a used one it will only save you maybe $50-100, and then unless you meet up with the person you will run the risk of it being married already.
On another subject I didn't quite understand I you were going to buy an access port or have it pro tuned to stage 2. From what I have seen and heard, unless you are going to BIG numbers(400+ whp/wtq) everyone seems to love the access port. Mainly for all o the functions it has, even though it is more expensive than the average pro tune. I personally am about to order the cobb stage 2 package coupled with a catless up pipe and K&N short ram intake. Hoping for the same outcome of a nice little growl at idle and cruise and then a real head turning for spirited driving.