I've looked at the commercial version twice, here's about how it shook out for me:
Under the old E-smith (before Mitel acquired them), the price for the commercial version was quite reasonable, and even fairly affordable for small business users at around $500/year, IIRC. I was about to pull the trigger on this when Mitel bought E-smith. I waited about a year to determine that e-smith was really a going concern, then checked with Mitel about a supported version.
The price had roughly tripled - It was going to cost over $1500/year for supported SME, and even worse, I couldn't deal directly with Mitel, but had to go through a damn reseller, most of whom (sorry to say it) were either not all that competent, or had significant attitude problems. My research showed that very few of them could be counted on to do anything but take your money and deliver the commercial SME server CDs. (I'm sure there were exceptions, but I heard some real gripes from the handful of users I contacted.)
I really think Mitel shot themselves in the foot here w.r.t. both pricing and especially, the hands-off, you-must-deal-with-an-authorized-reseller stance.
I even considered becoming a reseller myself, but I didn't really want to resell it, just use it for a few clients that needed it - and most of my clients don't hire me to do that sort of thing - to be honest, I'm a very expensive sysadmin, and a multi-purpose server is more likely to be a peripheral need for a guy that specializes in new technology development.
As a result, niether Mitel nor E-smith ever got a dime from me, although I would have been more than willing, if they'd offered a reasonable deal. Too bad, really.