I went the DIY route as well; all the COTS options i looked at were just too expensive for me.
I was installing my rack into an existing closet and needed rear access, so I took my MA Slim-5 rack and added about $40 in parts from the Depot:
4 heavy duty fixed casters
48" 3/16" 2x2 angle
Additionally, the bottom of my closet had a lip i had to get over, so I made tracks with Uni strut and shallow U channel.
Since I was pulling it out onto carpet, I made a set of track extenders that I just stow in another closet when not needed.
It works very well even with a fully loaded rack and all together cost me about $70 and a couple hours of time.
I didn't really take the time to make pretty (other than spray painting the angle iron and hardware black) since the only time any of it is visible is when I do any rewiring.