How much to install a stereo system?

Hi, im hoping to get a stereo system installed in an '04 nissan xterra. i have a sub box already, from an old vehicle i used to have. Now, i already have a deck now i want an amp to connect the box im planning on about a $150 amp, i need to get the box mounted, in the back of the xterra, and the amp mounted, connected, to the deck and the, box. how much would it cost to connect everything? Car Toys? Best Buy? Quality Auto Sound does $1 install but not on an entire system. HELP ME! thanks