You don't always have to go with the exact number of pins.
For example, standardize on 10pin and 20 pin ... instead of 28 pin, maybe go with 1 x 2x5 pin + 1 x 2x10 pin ribbon cables.
10 pin is very common (ex usb 2 headers) so being so mass produced they're also very cheap.
20 pin is also common (usb 3.0)
There's
29400+ 2 row 0.1" spaced headers :
https://www.digikey.com/short/pdpp3m2965 2 row 0.1" spaced with shroud :
https://www.digikey.com/short/pdpp81rows pins count:
- 2 06 : 75
- 2 08 : 52
- 2 10 : 384 (cheapest 0.18$ at 100pcs on Digikey)
- 2 12 : 45
- 2 14 : 276 (cheapest 0.21$)
- 2 16 : 277 (cheapest 0.26$)
- 2 18 : 13
- 2 20 : 350 (cheapest 0.31$)
- 2 22 : 6
- 2 24 : 110 (cheapest 0.48$)
- 2 26 : 255 (cheapest 0.26$)
- 2 28 : 1
- 2 30 : 137 (cheapest 0.48$)
On Digikey, you have ribbon cable at
50$ for 20 wire 30.5m ...
63$ for 24 wire
63$ for 26 wire
69$ for 30 wire
85$ for 40 wire
You can probably get much cheaper on lCSC or other distributors, or at bigger rolls... but the idea is you get the best price at 20 wire 2x10 or 40 wire (2x20)
115$ for 152.4 meters of 10wire , 180$ for 152.4 meters 20wire ...
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edit: also, you can get round pins and solder them to a tiny board to simulate the regular pins of a DIP chip :
https://www.digikey.com/short/pdp4pj