Pattern classes represent the pcb complexity and will affect the price.
Higher class means higher manufacturing cost. Unfortunately it is not practicable to present the cost increase in numbers as we would prefer to have full access to the entire manufacturing files to make a reasonable assessment.
For example, a big sized PCB with 150 micron track may be more complex than a small PCB with only 125 micron track. Most of our factories currently manufactures printed circuit boards to the standard price of class M6. Please note, all dimensions in micrometers (microns).

Pattern classes M5 M6 M7 M8 M9
Annular ring, hole -pattern outer Layer Pad >200 >165 >140 >125 >100 A
Annularring, hole -pattern inner layer pad >150 >140 >125 >100 >75 B
Trackwidth -inner -outerlayer >200 >150 >125 >100 >75 C
Insulation inner -outerlayer >200 >150 >125 >100 >75 D
Insulation -innerlayer to different net >355 >300 >250 >200 >190 E
Clearance soldermask -soldersurface >100 >90 >75 >50 >50 F

Pattern classes, reference views: