Get used...
You can easily find a Lion capable Mac Pro that is from the 2008 era for $900-$1000 on ebay. Since you seem to find it okay to be using a G5 (your computer could be anywhere from 6-9 years old at this point), I would imagine using one that is ~2-3 years old would be just fine and a decent step up from your G5.
I have direct experience with this, having used a G5 from 2005 right up until 6 months ago, along side a 2006 Mac Pro (1,1). That Mac Pro has a significant boost in performance over the 2005 G5.
It seems kind of pointless to remark on MS's wide hardware support if it turns out you don't use/can't stand their decisions when it applies to your particular use case as an individual. It's stunning how often this canard is used to help support why using MS's OS's, it's like saying, "Denny's is the best restaurant because so many people go there for a meal."
Biting the hand that feeds IT
