Budget 2-player online Steam games from the past few years?

So I've got a buddy who moved away that I'd like to play some online games with. Either 1v1 competitive or 2-player co-op, and we're probably going to play infrequently, so continuous narrative or super long campaigns is maybe a downside. So probably not feeling anything like Original Sin 2, despite it apparently being pretty fun in co-op. Also looking for something kinda on the cheaper side, if possible.

I can't really distill down the gaming interests of myself and my friend very easily, though in recent memory we've played Civ V and Twilight Struggle (that Cold War board game) together. I'm thinking of trying out Armello with him, but I'm also willing to look outside the strategy genre. Just so long as the multiplayer is easy to get going and not some "open a bunch of ports on your router" nightmare.

Helldivers is pretty dope for only $20.

@bisonhero: Perhaps River City Ransom: Underground could be your thing. It was rough when it came out, after 10+ patches its actually quite good. Perhaps check it out if you find the time.

It's currently full price (well, $50) but if you're into hyper ridiculousness (and third person shooters), extremely B-tier cheesy acting, a lot of explosions and general chaos (and Giant Insects to murder), Earth Defense Force 4.1: The Shadow of New Despair is my favorite game in existence, currently. A friend of mine got a new computer just as it went on a mid-week sale for like $25, and shortly after our first session I went and got every piece of DLC plus the two bigger mission pack DLCs (they're definitely not needed, but I needed them). Knowing what I do now, I would totally pay full price for it, but for others I would say wait for a sale, unless you're familiar with EDF and have enjoyed it in the past.

It's lengthy (they added 9 missions to Multiplayer so it's up to like 98 or something in total), but it's the kind of game you really can just hop in and out of easily. The menus are a bit odd, since they're WASD based, but then to invite people you have to use the arrow keys to bring up another menu that has an invite option, but once you've done it once it's easy to remember. Also it's the type of game where it's set up for you to play the difficulties in order so you can't really jump into the highest difficulty immediately and make your way through (though you can skip to Normal and be fine).

Other than that, Halo Wars is a pretty excellent RTS that's on Steam, and that game has a pretty good co-op mode. Both people control the base and can give control of units to each other so it's good to have someone handle base management and someone else on unit duty until the base becomes pretty much self-sufficient. I had an excellent time with it on Xbox with another friend, and sometime later I got it on Steam and it runs pretty well. Looking it up, it's currently $20. I'm not entirely sure how easy multiplayer is to start on it on PC, though I don't think it would be too hard.

A.I. War: Fleet Command is yet another good (and cheap! $10 for the base game, or $17 for the game + the dlcs which are pretty good) RTS game. It has a relatively steep learning curve, though, and the UI wasn't great from what I remember, but a friend and I had fun with it and kept playing for a good while. The one thing is that I can't remember if there are fiddly port things you need to do with it, as it's been a while.

There's also Magicka, which basically all of my friends dislike but I loved it. I managed to rope one or two into playing a few times and had fun. Trine is also a good side scrolling romp.

...huh, that was a lot more than I first intended on writing. I hope it helps! EDF 4.1: The Shadow of New Despair is amazing!