How much would it cost to a install a radio I already have on a 2012 Nissan Altima 2.5S sedan.

It really depends on what you have and what you need like antenna adapter stock harness stuff like the dash kit that That might cost a bit for that car

Well it depends on if they have to get all the wires to hook it up. I've had them bypass the stock amp in my 04 Ram and ot cost me $80 to $100. They also did my step sides on my truck but i paid $352 for the install and the purchase of the step sides.

Depends what your doing we paid lil over 300