I have been recording my band for many years. For anything serious, we have it professionally mastered here in Chicago or New York for $100-$150 per song. Those guys are using gear that would never make sense to own, and (more importantly) have the experience to get things sounding as close to "radio-ready" as possible.

Back to the original poster's question... Which mastering suite/plug-in is best suited for BIAB/Realband? If you're happy with the overall sound of your mix, you can just run it through a peak limiter to get things a little louder. Look at kvraudio.com for free peak limiters. This one is highly regarded:
http://vladgsound.wordpress.com/plugins/limiter6/.

I use the Izotope Mastering Essentials. It's included with Mixcraft Pro Audio 7, which costs less than half of Izotope Ozone. Essentials doesn't include nearly as many features as Ozone, but has a lot to offer in terms of shaping the sound and amplifying your mix. That, and Mixcraft is a great DAW if you need features that extend beyond Realband's capability (I use both).

Lastly, here's some great general advise:
"The short version: Stop recording so hot. Instead of trying to get your tracks to peak at -2dBFS, have them peak between -20 and -12dBFS and your recordings will almost undoubtedly sound better. Mixing will be easier. EQ will be more effective. Compression will be smoother, more manageable and predictable. You're in the age of 24-bit digital recording - Relax and enjoy the headroom. Even if your only concern is the volume of the finished product (which would be a shame, but it happens), recordings made with a good amount of headroom are almost undoubtedly better suited to handle the "abuse" of excessive dynamics control. QUIETER recordings have more potential to be LOUD later. It's because they're usually better sounding recordings in the first place."

John Scrip - MASSIVE Mastering
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I hope this helps!

Best,
Mark

Mark
2020 BIAB Audiophile, Mixcraft Pro 9
Band: http://www.midwesternlull.com