I have Sonar Platinum.. About to do a Bonamassa style blues song.. Will do the bass in my Fishman Triple play midi enabled guitar.. What is my best option for a realistic bass tone? I want to think Platinum has something for me but I am willing to spend few dollars for 3rd party VST instrument...

Thanks in advance

I use Scarbee Jay-Bass religiously for midi. If you don't have or can't afford Kontakt there is a free Kontakt player that will allow you to load the librarys and play them. Native Instruments has a selection of great bass librarys for Kontakt. I just have always liked the Jazz bass. They have a Precision as well.
I mostly play the bass myself on a Fender fretless Jazz bass.

I agree with Sidroe. Scarbee Jay Bass all the way however, I process Jay Bass through Overloud Mark 2 bass amp and the sound is even better.  Add a bass room patch from Breverb and the results are stellar!

Check out the bass in studio instruments which is bundled with Sonar. It quite good.

If you do want better then I would also recommend the Scarbee basses, Orange Tree has some seriously good basses but they need the full version of Kontakt.

For me, apart from playing the bass myself through various bass sims, Spectrasonics 'Trilian' is the shiznits

I also use Mark Studio for synth or real bass tracks. I used to use Audiffex Gallien Krueger Pro but Mark Studio has won out. Adding any amp sim to your bass track will do wonders.

I also noticed you said you were going to play the bass part on your Fishman. If you are capable of doing that why not invest in a good inexpensive bass guitar or borrow one from a friend and REALLY play the bass! A four string bass is nothing more than the lower four strings on the guitar. Even a cheap bass thru an amp sim would sound worlds better than a sample or synth bass. To me, what makes the any instrument like bass or guitar is the inherent noises and the glisses and slides of playing that instrument. The character of the instrument is the noises that go along with the performance.
I think you would find the playing of the real bass changes the way you perceive the bass part itself. I have always found this to be true.