Cheapest way to get higher density PCBs

[790037918]

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[IconicPCB]

You want to play with professional grade components You need professional grade interconnect system ( read PCB).

Your other option is to mock up bga chips from lego blocks and use a phenolic single sided PCB.

Quality is like oats.

Once they have been through a horse they cost a little bit less.

[suicidaleggroll]

I don't know what's available in China, but in the US OSHPark has 4-layer boards with 5 mil trace/space and 18 mil vias (10 mil drill + 4 mil AR) for $10 per square inch for a set of 3.  That should be fine for 0.8mm pitch BGAs, unless you need a bunch of impedance controlled traces, in which case the 4-layer and pre-preg thicknesses start to fight you.  I can't imagine you are unable to beat those prices in China.