i had a shop do my work too. I would recommend a pro do the downpipe. you don't want that messed up. they ahve to disconnect the O2 sensor and it bolts right ot the turbo. you don't want some goofball messing that up.
the exhasut is plug n play. a not so nice guy could do it. i paid $60 to have the exhaust installed. i forget what i paid to have the dp put in. $250-300??? i honestly don't remember.
you should easily get an indpenendent volvo shop do it all for under $500.