Amiga 512kB memory expansion. Minimal cost efficient design.
I've decided to open source my design after building few batches of these. Two versions of gerbers are available, single and panelized version which fits 4 boards inside 10x10cm area (many china pcb houses offer cheap deals on custom panelized under 10x10cm boards). Should work on all A500/A500+ machines Rev.3->Rev.8
(older Rev.3 and Rev.5 boards pre 8372 Agnus did not toggle DRA8 fast enough, so there might be incompatibility issues on older Agnus versions, but for me my Rev.5 board works nicely with the DRAM mentioned in BOM below (https://eab.abime.net/showthread.php?p=1379222))
Ordering 10x4 boards with required parts from Ali or other cheap sources (16.7.2020 status) total was 62euro. So 62/40 would be 1.55euro per piece. But of course that doesn't include the cost of solder paste or flux, but even if you calculate them in it still will be under 2e.
For 5x1 (min order for most cheap pcb houses) price per board is of course somewhat higher due postage per piece is higher, but should still be around 5-6e.
Cost of time soldering and testing the boards are not included in estimation :-)
Soldering SOJ-42 is painful for beginners unless you have good preheat and/or heat gun setup.
Backside has also spot for optional led, but I've never populated it as I don't see any use for it.