Exciting project!
For motor cost, you won’t do better than this. 2208 size, $30 shipped for 16 of them. They are 1450kv delta, so can be converted to ~850kv wye (though not easily because the base blocks access to the wires plus there is epoxy).
For controllers, Lepton is designed for low cost. 10A in its basic form, but should be higher with my modifications to eliminate the places where the PCB copper alone carries the high current.
However there are only enough of the special MOSFETs left in stock for 9 of them, so it may require negotiating with me and Valentine (plus some SMD soldering) to scrape together the last few that you’ll need 
It also does not have current sense, so if the voltage-based torque control is not precise enough then sensors will need to be added. There’s a pretty good chance I’ll end up doing it myself regardless, so just say so if you want me to hurry up.
I also wanted to do multiple motors per MCU to save cost and size, but after seeing that the STM32G01 is barely over a dollar, and coming up with a compact design where a single pair of fat power wires runs axially through the input holes in a stack of single-motor boards, I decided it wasn’t worth the trouble.
If you don’t have a CNC machine, I would recommend getting one if at all possible. It’s so nice being able to machine real high performance parts rather than trying to design around what is available. And simple things like figuring out how to screw down a brushless motor can incur a surprisingly high complexity/weight penalty compared to having the bearing tube/stator mount integrated into another part.
Teflon sheet is a miracle for low speed bearings. A thin 2mm wide strip can replace a big heavy ball bearing, and significantly reduce the size and weight of the part that holds the bearing too. But it does require very tight tolerances. Possibly doable with 3D printing, but this is another reason I love my CNC.