Unfort. XSI is rather pricy.
Well, 500$ for Foundation. Imho for a software that did tend to be like 6k, is not bad. I purchased as great global solution for an indy artist (GI rendering, character animation, etc)
And those foot glued to ground with the touch of a key.Its bones and ik basic tools are so well done that for a similar rig in Blender I need to work hard till I have a nice rig. Even so, it does not get even near to xsi speed of use etc, in that area.
And even so, imho you can do way more With Blender character animation than with , for example , CFX.(and similar tools) You can use copy location and rotation constrains, you can use its automatic IK -that works quite well- you can use its paint weihts tool, you can use its new envelopes, limit ik angles rotations, use empties or bones with track to or similar constrains, and a way long etc.
In Character fx, is , yep, very, very much more simple to learn, direct to the point, and imho is a great tool, but once you want to animate with a bit more of functionality (and trust me you want to be able when doing some serious animation, to glue things to world cord space, not only feet, but also a hand in a fence, in a branch, etc, etc) you find cfx only allows weights asigning and location+rotation simple bone animation.
It all works straight and its x, md2 and b3d exporter are functional and good. But you will at some point probably want better animation tools.
In xsi you can configure all your keys. I do have one to trigger "pin object" , which allows me to glue feet without compromising my rig or its fk/ik. And that counting I don't use th epremade character rigs, but i do all with basic ik bone chains, etc. Maybe as I am to used to raw bones stuff and constrains, helpers, etc. As whenever at work I don't use Biped, I build my self so my rig(helpers, constrains, IK, etc).And do so in any package.