there are plenty of FREE libraries out there which are just as good if not better.
I use Yahoo! UI. Other include dojo and mootools
use them.. keep it free
ps: there are hundreds of AJAX libraries out there.. a year from now a lot of them won't exist.. only a few will dominate. so why spend money on an AJAX library now when it will (probably) be non-existant in a year? use the free stuff.. wait for the playing field to level out and the dust to settle.. if a commerical AJAX library dominates in the future buy that one.. for now just use the free stuff