I haven't used DD logs personally but from what I've been told if you send the majority of your logs straight to archive to an S3 bucket and only rehydrate the logs when you need to access them their pricing is pretty reasonable. Because you're storing the logs in your S3 bucket you can keep them however long you want and rehydrate them when you need them (say 30 days later).

The bill will still be in the low thousands but paying 30-40k per year for a logging solution is probably worth the cost if it means you don't have to maintain it. Having logs and metrics (and the APM if you're using it) all in one place is _really_ nice.