CubeSat

https://en.wikipedia.org/wiki/CubeSat

Cost to build: $50k. Cost to launch: $50k. Falcon 9 intendes $1200/lb launch cost.

Basics are 100kg fuel+rocket per kg of payload [1].

Smallest rocket to reach Low Earth Orbit was JAXA SS-520-5/ [2]

The current trend is reusable rockets, to drive the cost down significantly. The limit of space flight cost would thus be fuel only. For example, a ton in space would cost 100 tons of fuel. At $2/kg [3], we have a space trip cost $200k in fuel for 1 ton to space - or $200/kg.