I just finished the design of A New half-sized Pop Bumper Driver Board intended to be a drop in replacement for the original System 80 Gottlieb design. Fixes many of the design issues present in the original design including many Best Known Methods posted @ Pinrepair.com.
I have decided to release this design under to the public under the TAPR Non-Commercial Open Hardware License which indicates:
You may make products based upon this design, provided you do not make more than ten units in any twelve month period for your personal use.
BOM costs are under $11 not including the PCB. The PCBs are less than $28 from batchpcb.com and a link is included in my Blog post.
Please check it out at:
http://pinball-mods.com/blogs/?p=4 The rest of the site is not complete; so please make sure you use the link above.