Why DAC ic costs as much as a clone arduino
Analog is expensive, by and large, and a 12 bit part (if it actually does manage 12 bits) is actually a surprisingly high precision component (1 part in 4096, it is probably laser trimmed), and due to process issues both requires processing different to that used for digital stuff and in ways that tend to be fab specific. 

A relatively simple microcontroller on a not very fine mask geometry (Those things are very far from state of the art) is the sort of thing that any random cmos fab can probably run, and it does not need laser trimming (Takes time per component).

Now depending on what update rate and precision you need the obvious thought is to use one DAC, some analogue switches and caps, maybe plus some opamps to drive multiple outputs, for example you could use a 74HC4067 plus 16 small caps to drive 16 high impedance signals from 1 DAC, time division multiplexing the updates and holding the voltage on the caps between updates.   

Volume also matters a lot, look at pricing when you buy whole reels of parts (and not from Mouser either), rule of thumb is that the full service distributors (Mouser/Digikey/Farnell/RS and the like) mark up by about 100% or so for the convenience, if you buy in quantities sufficient to interest the field sales guys you tend to get MUCH better pricing. 

Needless to say the guys making cheap ass arduino clones are buying multiple reels of parts at once and are not shopping at Digikey, they will also likely accept a rather higher part failure rate which can again make things cheaper if you are prepared to shop grey market in Shenzen.