Where (or when) to buy AoE2 DLC on sale?

So, a bit of background- I've owned the HD edition for a year or so now, but only recently have I actually sat down to play it, and have really enjoyed it! Bit of a steep learning curve for someone not really into RTS games prior to this, but I'm slowly getting better and have managed to beat the Moderate AI a few times.

Problem is, though, I play mostly with my friend, who has all the DLCs and usually sets up games with those settings. I don't have any of them, so I can't do Megarandom or play any civs in multiplayer beyond the daily rotation. He says they go on sale for like one or two bucks all the time, but it seems like the last time that happened was the Steam Winter Sale. Is there anywhere currently I can find some of the DLC for cheaper than their current ten bucks apiece, or when do you expect the next sale will hit?