Interestingly, Salamander has allowed for rack rails to be installed on their Synergy racks for years and years. The problem is that they don't really catch, in their designer, that you can't put in rack rail AND doors! I mean, who would want a door on their rack mounted gear right?
Seriously, Salamander makes some decent stuff, but it isn't great, and it is super pricey. I use it from time to time, but I typically prefer what you can get at racksandstands.com or other online etailers for far, far less money.
Plus, you can pick up a fairly inexpensive rack, like this one:
http://www.racksandstands.com/Wood-Technology-AR-43-O-WT0295.html
and put rack rail into it for under $500 total.
Of course, rack shelves (custom) are about $100 per shelf/component.