About a year or so ago, I switched to the bulk generic strings from JustStrings.com. Honestly, they're pretty good.

Rotosound set of four plus two singles for my 6-string bass are US$34.39/set plus shipping.
Bulk generic (come 6 strings per package each gauge) come out to US$14.94/set plus shipping.

Since I no longer make any money playing, that's pretty easy math for me.

To Simon's point, I have never checked the consistency of the strings with a caliper, but I've not yet had any tuning issues with them, and they play and sound great.