Economical way of manufacturing PCBs
As for the cost: 4878.23 &lt; 4994.26 so that is simple.

The 4-layer option is about 2% more per product. 
You don't tell us what type of product it is so I can't really judge, but I would go for the 4 layers as it will get a much better power and ground grid. Moreover with a continuous ground it'll have more chance of passing EMC.