Depends on how many you need. In Canadian dollars I think anything <$50 is a good price for a segment, but they're very rare domestically. In the US it's A BIT easier, in Colombia I find it very easy. Super sale fares on Avianca still earn me segments, so I've done that a few times, just gone to a city for a day or 1.5 days while I'm already on vacation in Colombia. Nice way to explore too.

In Europe I can't speak to the prices, but it might be tough. The cheap flights won't earn anything, you'll have to fly legacy carriers and even then I'm not sure the earning of segments. Basically It's not really easy to find a segment run, better to do is find a good fare then add segments to it via ITA.