I designed a PCB that combines a DIN x4 and a DOUT x4 on one small PCB.  The modules are connected by traces, so they'll work together in series using the PCB connection, or the board can be split in half so the modules can be used separately.  The board is less than 10x10cm, so it can be printed extremely cheaply at places like DirtyPCBs (~$16 for 10 boards) (I think SEED is offering even cheaper 10 packs of 10x10 boards as well now, but I haven't tried them yet.)  Resistors are mounted on the