Bandwidth monitoring

I am still having trouble getting bandwidth monitoring (and alerting) working with The Dude. While Googling around for answers, I found this app recommended for the job;
PRTG Network Monitoring Software

I have installed it and have been running it for a week now.
Very nice in a lot of ways. Sadly, super super super crazy expensive.
I am on the fence if I should continue to run it (and thus learn it) after the 30 day trial in its limited free instance.
I was thinking of running both this and The Dude. The Dude does everything else, this just does bandwidth monitoring for 100 links – The free version is limited to 100 sensors.
Duno. On the fence. I would rather do everything through The Dude and just to get to know it.