Yeh, the transmitter and receiver have to be on the same circuit for this to work.
Mesh seems good, but can be expensive. Apparently, Google's mesh system is great but yeh, pretty pricey
EDIT: Also, not sure I would trust a Powerline adaptor system given the segregation required between data and power to avoid interference. I'm sure it can get you out of a tight spot, but the speeds would surely suffer running along the same line as 240V