I did some more research on mini/microquads as I worked on building my ~$18 version and actually found some very strong prebuilt options:

$39 WLtoys V939 Beetle 2.4G 4CH Quadcopter Dexterous Mini UFO BNF

This one is ‘Bind and Fly’ you can bind it to the Turnigy 9x remote. Its a micro quad so flyable inside and, in light wind, outside. Very similar to the $18 quad I’m building; but already built!

I purchased a V939 and have played with it a bit. Its fun but compared to other models it certainly isn’t my favourite. Still, given its small size it is likely the best choice if you plan to do mainly indoor flight.

$39 Syma X1 Series 2.4G 4CH 4-Aixs RC BumbleBee UFO Micro Quadcopter

A mini-quad, a bit big for indoor use but actually quite usable outdoors. We purchased a few of these at work and they are surprisingly robust (though given our abuse not indestructible). If you do break something spare parts are quite reasonably priced which is nice.

Includes a remote but can, apparently, also be bound to the Turnigy 9x if one desires.

Having now tried additional models; I’d say the X1 is a good introductory quad but you are likely to outgrow it pretty quick. The cost still makes it appealing but if you can spare the extra $10 I’d get the v949 listed next.

$52 WLtoys V949 Upgraded V212 2.4G 6 Axis RC Quadcopter RTF Mode 2

Again a mini-quad, the general design/parts is extremely similar to a pepped up X1 but this unit comes more highly recommended as the flight controller board is apparently notably better as is the included remote.

Unfortunately, you cannot bind this quad to the 9x as it isn’t a compatible protocol. Otherwise looks like a great choice. You can upgrade the propellors to GWS EP 5443 for front and back to notably improve the performance.

Having played with this one a bit I’d say its the clear winner if you’re looking to just purchase something with a remote. The only nock I’d give it is the lack of 9x remote compatibility.

$32 WLtoys V949 Beetle RC Quadcopter Mini UFO BNF

This appears to be a previous generation V949 and will bind to the 9x remote. Being bind and fly it doesn’t include its own controller. It seems like this one is getting difficult to find; I’d probably pass on it given the difficulty in being certain you’ll receive a 9x compatible unit.

$33 V929 Beetle 4-Axis Dexterous Mini UFO BNF

This appears to be a two generations older V949, largely parts compatible but the older electronics will talk to a 9x transmitter. If you have a 9x transmitter I’d recommend this quad as its definitely compatible. I’d upgrade the props as per the v949 with GWS EP 5443 for front and back.

Overall its quite fun to fly but the auto-flip is a bit annoying. I’m going to adjust the rates down a touch to try and avoid auto-flipping but I’ve also ordered a replacement brushed MultiWii controller to try out which aught to enliven it even further.