Can anyone tell me if I can buy a return ticket, and if so does it work out cheaper than 2 singles?
IF you can buy a ticket at the bus station, then you can usually buy a return one, but it's not cheaper. Of course, it may happen that a specific bus company has such an offer (it's not frequent though), but you need to check it on their webpage.
Sometimes it's possible to buy a ticket online, then it may also be possible to buy a return one at once.
On a bus it's not possible.