The price of your Brick Pic will depend mostly on it's size. When creating your design in the Brick Me Creator, you can see the total price of your mosaic at the bottom of the page.
The mosaics are created using either small baseplates (24x24 studs) or large baseplates (32x32 studs) which cost $17 and $30 respectively. For example, a 2x2 mosaic using 4 large baseplates will cost $120.
There is also a 5% premium if more than 25 colours are used in the design, and a discount scheme that gives you a higher discount the larger your mosaic is.