Their small quantity prices seem to be reliable but their volume prices are all over the map. Like I posted last night, the site was quoting $13 for 500 2 layer boards 100mm x 100mm. So unbelievable that I refreshed my browser and tried again, same price. Tonight they're quoting $500 for the same boards. Also last night, within the space of an hour the price for 5 four layer CI boards dropped from $108 to $81. And 100 of the same board was only $102. Tonight those prices are back to $108 and $246. Most of the other prices are 3x what they were last night.
I don't know if it was just a quirk with the website but others (ie. pcbway) seem much more consistent. By the way, with pcbway there is less than $50 difference between 4 layer CI and 6 layer CI for 5 boards.