How do you organize your ads?

I work with a small company that runs five websites that run ads with five different ad networks and it can be a hassle staying on top of which network wants to fill for the month, which networks eCPM just dropped, managing mobile and specific geo requests, and then how the networks default to each other.

Most big ad servers look great, and support 110% of the features I could ever want, but they also charge insane amounts. Google DFP is free (to a point, then crazy expensive), but seems super complicated.

All I really need is one place to organize my placements, be able to dynamically control them so I can default from ad networks without updating code with them, and... that's basically it. We don't sell ads or run campaigns, just 3rd party networks.

How do you guys manage your ads? Do you use an ad server? Do you just waterfall it between the networks?

inb4 lol adblock