I currently use Pastel Pencils which allows for great detail 
Price is for 1 subject.          Price for 2 subjects   With backgound
No background                       No background
5x7 - 50.00                                     75.00                                  125.00
8x10 - 75.00                                  125.00                                  175.00
11x12 - 125.00                               175.00                                  225.00
16x16 175.00                                 225.00                                300.00
16x20 300.00                                375.00                                425.00
custom sizes can be done: pricing depends on size and subject.