Working exclusively within SONAR Producer, Sonitus EQ has two different hum reducing EQ presets and R-Mix (from X2) has a "Noise Cancel" section.

Vlada,
 
If you can't retrack the bass(which really is the best option), I can help you with the hum removal.
 
I have Isotope RX3, which can do an amazing job on this type of problem. I say "can", because I have found instances where I can't clean up a track as well as I'd like. This usually involves trying to clean up a 2 track mix, such as old vinyl or tape. 
 
No guarantees, but if you'd like to send me the track, I'll see what I can do with it. 
 
Send me a pm.
 

I agree.... retrack it..perhaps with a bassist that has a better bass or amp. Why spend hours of your time trying to clean up his mess? 

If you can't re-track it, then just write it out and have the midi handle the bass part. A real bass is best though. Good luck!

Well looking at the responses here, until we hear it we don't really know I guess... As always everybody has different assumptions and experiences and therefore come up with different solutions and methods, one person says that works, another person says no it doesn't but this works instead. So this proves there really is no right or wrong and people do things different. such is the nature of things... You can't do noise reduction by committee :)

+1 to what Cakealex said. Without hearing it we can throw out a lot of generalities that may have varying degrees of success or failure. Sometimes we "luck out" and that hum is an exact 60 hz text book example. More often it contains several frequences that sometimes overlap what you want to keep. There are so many ways to approach this. I once solved a simlar problem by using a high bass filter to take out the hum and with it a good part of the bass itself. I then used a sin wav to reinforce the bass. That worked on that particular one but failed miserably at other times. I think times like this are good learning ops. Try to fix it several ways. Try sweeping in quadcurve. Try using something like audacity. Compare results. You never know until you try.

Perhaps multi-band compression is another option to consider?
 

Another workaround that may work for you is to shift-drag the bass track into an empty MIDI track and use that track to feed a soft synth bass. Depending on the playing style that was used, this may or may not be effective.

mettelusAnother workaround that may work for you is to shift-drag the bass track into an empty MIDI track and use that track to feed a soft synth bass. Depending on the playing style that was used, this may or may not be effective.

And if that doesn't work, try doing AudioSnap on it and generating MIDI using RMB-click (context menu on the clip, not the clip header) Copy to MIDI.
 
If either of these work, they'll come pretty close to preserving the performance.

Try the R-MIX SONAR and use only the "noise cancel". It Does magic to noise and humming but it may also affect the transients