These are some parts and motors I've ordered. Not all have been vetted, but this provides a record of their source.

Motors

Type Price Source Notes
n20 6v 500rpm $1.97/ea https://a.aliexpress.com/_mNLg48i
n20 6v 300rpm $0.68/ea https://a.aliexpress.com/_mP0aLKa
"Spicy" n20 $0.55/ea https://a.aliexpress.com/_mPVpUeA
"Spicy" n50 $0.81/ea https://a.aliexpress.com/_mMmHJMQ
ChiHai 16mm 700rpm $12.55/ea https://a.aliexpress.com/_mLiNOYK
Emax 1104 4300kv $1.70/ea https://a.aliexpress.com/_mqh2Aie
20mm Planetary w/130 motor $1.20/ea https://a.aliexpress.com/_mtMWO6e
"Spicy" 030 $0.45/ea https://a.aliexpress.com/_mOF3498
"Spicy" 050

Electronics

Type Price Source Notes
FS2A $8.30/ea https://www.aliexpress.com/item/4001112099097.html
Brushed ESC $3.80/ea https://www.aliexpress.com/item/4001281617740.html