, as @Asteroid
mention, a cheap 580ex will work.
Actually the 80d you have, has wireless optical master function on built in flash, your choice of flashes for off camera ttl/manual flashes are 550ex, 430ex/I/ll/lll, 580ex/I/ll, and the 600ex rt.
Some yongnuo models are compatible as Canon ttl slave, 565ex, 568ex, 600ex, 685ex.
There is one downside of the build in flash master function, it is not hss capable, but you can get a old Canon st-e2 ir transmitter, it is also cheap.
Canon 550ex, 580ex l/ll, 600ex, and yongnuo 568 ll/lll, yn600ex ll, are capable as on camera wireless optical master control, HSS mode also work. So you can get two or more flashes if you like, one as on camera master, others are OCF ttl slaves.