What I've found is that the monitors are good for hearing every little thing--important when you're trying to make subtle changes-- but the cheap speakers might be better for mixing. My last step for each section of a track is to play it through the cheap speakers and adjust the mix. Once it sounds good there it will sound good everywhere. Even if it sounds better on my monitors to do it a certain way, I'll do whatever sounds best on the cheap speakers. Then I flip back to the monitors and it sounds great. More importantly it will sound good in cars, on laptop speakers, and so on.
My cheap speakers are a pair of
these running with
this amp. They're little 4" midrange-heavy speakers with no bottom end and no tweeters. This $50 combo seriously improved my mixes more than my $500 monitors or $200 headphones. Professionals often use Auratones or similar speakers--these are the same idea, just a simple speaker that focuses on mids. You could get the same effect with a laptop speaker or one of those $10 bluetooth mono speakers they sell for iPhones.
Don't use them to mix sub-bass, though.