The cost depends heavily on who does it, whether they use pre bent tube or bent from scratch on site, whether they use regular tube or stainless steel. It can definately be a "you get what you pay for" type of deal. So figure out what you want, then call around. Most good shops can give you a ballpark.
For the X-Pipe question, here is a link that explains it and the Tri-Y better than I can.
http://e30m3performance.com/tech_articles/engine-tech/x-pipe/x-pipe.htm
