Hi,

there is no virtual environment I am aware of that works with AIX these days ... but a nice 43p 150 or a B50 or B80 should be affordable these days - and is enough to teach you the very basic administration of AIX.

But knowing how to extend filesystems or delete a user on AIX doesn't make you a system administrator ... AIX is these days so highly virtualized that you will hardly be able to teach yourself all the skills required to work as a system administrator in a mid-to-large size company with current technology with external storage, clustering, TSM backups, Tivoli monitoring and all the fun stuff. So I would highly recommed to get some formal training in the more complex areas like virtualization before you go for a job as a system administrator.
In addition you should have a solid background of other areas in IT like networking, maybe some hardware- and shell scripting skills - and the ability to live for days without food or sleep in case of tough production issues... So if you want to have a life or any further commitments (wife, children, personal interests) - don't take a job in a smaller company - be aware that being a sysadmin is in many cases a 24/7/365 commitment, a permanent challenge - but the greates job you can get - I can promise you it will never be boring at all.
Kind regards
zxmaus