I have a traffic source where traffic goes as low as $0.02 CPM, and can deliver tens of thousands of hits an hour with minimal difficulty.
On top of that, the traffic source does have conversions, except those conversions are on the order of 0.08%. Still profitable, mind you.
What cheaper tracking source(s) are there that would allow me to filter by geo, measure conversions by browser/os/custom variables/time/etc, and still be able to handle potentially 1 million hits/day?
Maybe ask them for custom pricing or maybe go with CPV/Imobitrax on your own install?
I remember someone testing high click volume with a modded prosper install on here a while back. Might be worth digging back up.
Our latest self-hosted tracker can handle the volume, and the current price is $99/month. We've got users running millions of clicks per day.
www.Thrivetracker.com
You can check out our thread on STM here:
http://stmforum.com/forum/showthread...form-by-iPyxel
Or contact us directly!
P202 is free 
+1 For P202. Been using it for 6 years and still going strong
Seeing as a lot of you recommend self-hosted trackers, would you please care to suggest servers to run them?
A multi-server mesh-networked tracking system would be ideal for me.
I'm thinking multiple round-robin DNS pointing to multiple load balancers with multiple back-end servers each feeding their own database.
I then have a cron job or some other periodic data-gathering daemon that generates the various reports I'd need without compromising the new data coming in.
That would suggest that when a new report is being generated, the server should be removed from the load balancer, the reports generated, then returned to the load balance before pulling off the next server, and so on and so forth.
What sort of maximum volume are you looking at data-wise?
Tens of thousands of hits an hour is doable on a single beefy dedicated server running an efficient tracker, which will save you considerable cost in implementation.
If you're looking to have something capable of tracking 10 million hits a day or so, you're probably going to be better off going straight to enterprise solutions rather than rolling your own, unless you want to do the whole multi-server load-balanced replicated tracking deal for interest as well as profit.
Absolute maximum volume is 2 billion hits/mo. (70M/day)
What sort of enterprise solutions are there?
The traffic is incredibly cheap, and very likely to have a ton of bots. The only reason why I'm exploring this sort of tracking is because some of my test campaigns turned a profit, but at the xxx,xxx hits/day level.
http://tech.bluesmoon.info/2009/09/s...mysql.html?m=1
This setup has a theoretical maximum of 700M inserts / day. But a record is 104 bytes, so my realized inserts using this method will almost surely be considerably less.