Well, I know a way to experiment with custom ICs without millions.
For 16nm and larger node sizes, sure. The lithography equipment needed is very mature and along with a fairly large number of Foundries doing non-cutting edge node sizes, very available and so the cost for masks is fairly low. Go down to 10nm, things are a bit more pricey but still basically use very similar litho tech that 16nm use.
Fact: For (mainland) Chinese-owned Foundries 12-10nm is as low as they go because they cannot buy the needed EUV litho equipment & photo resists much less produce it themselves.
5nm is a whole different animal that requires using EUV lithography. EUV litho gear is extraordinarily expensive and certainly not widespread -- you can literally count on 1 hand the number of Foundries using it. Chips using that node are high-value and high demand. There is no sneaking in a few test circuits per wafer because masks are just too freaking expensive and foundry customers simply will not permit 'other chips' to be produced on their production wafers.
