Cheap Kmart bike conversion to E-bike

[Someone you dont know]

So I’ve wanted to gift my eldest son by getting an E-bike for him I’ve got him a cheap bike off of Kmart unfortunately they don’t sell it anymore. Is there any parts i could assemble a bike with the previous bike for around 3 to 4 hundred AUD. I just bought a house so i cannot go anymore than  the given budget.

 

AUSTRALIA POST is potentially selling off there old e-bikes for $300 are they worth it rather than own made

 

requirements:

10+ kph

GPS and other stuff like that (optional)

as long as possible battery lifespan

is there is something that is needed please let me know

 

Thanks for anything,

Someone you don’t know.