You may be able to reduce your manufacturing cost by considering these factors.
1. Size and quantity of PCBs.
The cost of a PCB is determined mainly by the overall area. A more compact layout will reduce your cost.
2. Board material
Use standard FR-4 board material with 0.062" thickness and 1 oz copper weight. Choosing non-standard materials may increase board cost and delivery time.
Choosing non-standard manufacturing settings may increase board cost and delivery time.
See also: Low cost PCB prototypes.