If you want lots of tips on recyclable stuff to build from, you can look thru my build threads such as the DayGLo Avenger, CrazyBike2, Velcro Eclipse, Fusin Test Bike, Delta Tripper, SB Cruiser (my present ride), and the Flatbed Kennel Trailer builds Mk I - IV.
Kind of a lot of reading, but useful if you're repurposing stuff to build from.
Quite a bit of every one of those was built from recycled bits of other things, some of which came from thrift stores (and many of the bits that didn't probably could be found there if you look often enough).
There's a number of others here on the forum at least as good as I am at doing that sort of thing, but one of the ultimate ones is Naeem (numberonebikeslover), though I doubt he has any thrift stores there like we do here.
BTW, unless you don't weigh much, those little kids' razor scooters would probably be overloaded without some upgrades, perhaps a change in gearing (lower top speed but higher torque), though the parts might still be useful as an assist to a pedal bike. I've got one from goodwill that needs new batteries ( already did some repair work on it); there's a thread for it in the standup scooters section, though I haven't done much there yet.
I havea much larger scooter that was donated as parts that I've still got in the shed to work on--but here in AZ (or at least in my area of the valley) they're illegal to ride on streets or sidewalks (even though they sell these in stores, and I don't really see much enforcement of it, they *could* do it anytime). I only picked up the little one because my brother needed something for some of these huge mall parking lots to get from one place to another, that could be carried along in an Uber/Lyft/etc. The bigger one is too big for that, so it's only real use would be for fun on private land if I knew anyone that had a large enough area to ride it around.
But...it's parts *would* make a basic power-assist trailer, or even an assist for a bike (or trike), or a powerchair, etc.