Dahon k3 plus 16 has 9 speed cassette on 16 inch wheels with disc brakes for 500 to 600 dollars. But only available in Hong Kong. Under 10kg. You could probably put on a 10 speed 11-42 cassette with a 10 speed shifter and Shimano zee Rd, or else an 11-34t 11 speed cassette if it has an 11 speed hub, and double chainrings, altho the Rd is probably limited to SS short cage. It could probably fit in a regular sized regulation suit case without disassembly
