I really like the GK vsts. They dropped their prices several months ago. The current list price on the Audiffex site is $39 for the "standard" and $79 for the "pro". This is the first time I have seen a sale on the GK line since the price drop. JRRShop is selling the standard for $23 and the pro for $47. In my opinion that is a very good price.
You can download a demo on the Audiffex site so you can figure out for yourself if you need the standard or the pro. After playing with the demo I came to the conclusion that I did not need the pro as it just adds "dual" speakers and dual amps which I have never really liked on these type. YMMV. So demo it first before buying. Again, that is a great price on what I think is a very good Bass vst, but I happen to like the tone of GK bass amps.