When I built the main part before adding on it was around $1700CDN.  I was lucky and got a Q6700 when it was brand new for $250 instead of $1300 ( <3 Intel connections)
Since then I have upgraded..  8GB RAM, 2 more 750GB HDD, 1x 30GB SDD for Windows, added sound card to get off the mother boards, replaced two monitors, mouse pad, keyboard..   easily another $1100
And of course to top it all off if I want to upgrade I get hit hard..  need new mobo, ram, proc...   but of course I keep the old one together and use it at the same time.. so then it is once again a whole system