I think you have cause/effect mixed up a bit. Those cities are only "affordable" because people aren't there.
If a couple thousand people all simultaneously buy into an "affordable dense-ish urban area", that action would make that area un-affordable, and subsequently create all the same displacement/gentrification/nimby problems that follow. Your Detroit example is a good one, the dense-ish urban area now costs around $300-400k, because people already did what you've suggested. Unless your moving into lower-density mostly-suburban-ish areas in Detroit, your not really saving any money anymore.
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If your going to "Kickstarter" a city, let's make a brand new one. Find a bunch of empty land (greenfield or brownfield), and build a whole new dense city from scratch on it. This is easy/cheap to do compared to actual urban development (it's how all affordable suburban housing already starts), but just skip the suburb part and go straight from land to tall density, so there's no existing population to harm, no existing zoning issues to fight, no existing infrastructure problems to deal with. Go from nothing to 100% modern on day 1.
You could buy a bunch of land near say (picking a place at random) Hazelwood, Minnesota. Build your city with dense urban environment to start (enforce your own density rules, straight to 5+ story buildings). Fund an expension of light rail, and your just 30 minutes away from MSP airport by train, with direct flights daily to NYC, SFO, and SEA. And your already on I-35 freeway for freight.
There's such a shortage for affordable dense urban housing, that if you could provide affordable density with fast reliable transportation to existing cities (light rail to the closest major airport), your new city would likely fill up quickly, and help make these existing cities more affordable too.
I bet you're always the one in brainstorm meetings that says we need to rewrite everything from scratch, vastly underestimating the amount of work, bug fixes, and tribal knowledge that went into the existing solution in addition to the cost of building a new one.
This would be the modern version of the suburban development fallacy - building neighborhoods to a finished state with no method for organic expansion.
If a couple thousand people all simultaneously buy into an "affordable dense-ish urban area", that action would make that area un-affordable, and subsequently create all the same displacement/gentrification/nimby problems that follow. Your Detroit example is a good one, the dense-ish urban area now costs around $300-400k, because people already did what you've suggested. Unless your moving into lower-density mostly-suburban-ish areas in Detroit, your not really saving any money anymore.
--
If your going to "Kickstarter" a city, let's make a brand new one. Find a bunch of empty land (greenfield or brownfield), and build a whole new dense city from scratch on it. This is easy/cheap to do compared to actual urban development (it's how all affordable suburban housing already starts), but just skip the suburb part and go straight from land to tall density, so there's no existing population to harm, no existing zoning issues to fight, no existing infrastructure problems to deal with. Go from nothing to 100% modern on day 1.
You could buy a bunch of land near say (picking a place at random) Hazelwood, Minnesota. Build your city with dense urban environment to start (enforce your own density rules, straight to 5+ story buildings). Fund an expension of light rail, and your just 30 minutes away from MSP airport by train, with direct flights daily to NYC, SFO, and SEA. And your already on I-35 freeway for freight.
There's such a shortage for affordable dense urban housing, that if you could provide affordable density with fast reliable transportation to existing cities (light rail to the closest major airport), your new city would likely fill up quickly, and help make these existing cities more affordable too.