Affordable extension on a semi-detached home in Toronto

Hi,

I'm looking to build a cost-effective extension to my 2-bedroom semi home to maximize livable space.

According to the City's zoning map, I am located at: R (d0.6) (x736) - I hope this info helps.

My neighbour attached to me has extended his second floor out to the back already to include an additional bedroom.

I would like to either do the same, build a third floor, or do the same/extend the first floor out as well. In the end I would like to have an additional bedroom with or without an additional bathroom.

Is there a cheap yet effective solution to do this?

Much appreciated,

Marco