It would take a good pile of money to buy one of the original Bren Ten pistols. Lately, the name is heard quite a bit because a new company has been working on one that is supposed to be released sometime in early 2009.
The original Bren Ten was a commercial failure because the folks who built the pistol didn't make magazines for it-- they contracted with an Italian company to make the magazines, and then they found that they couldn't legally import the magazines... so they shipped new Bren Ten pistols to customers who had pre-paid and waited for them-- and they shipped semi-auto pistols with no magazines, but rather, a coupon for magazines!
The Bren Ten was also partially made famous by Sonny Crockett in the TV show Miami Vice who carried one early in the series.
I can't accurately answer all your questions... but they do show up on Gunbroker.com on occasion. Benefit to owning one? Piece of history, inherent collectible value. Of course, that value would be diminished as you shot the pistol. And if you were also lucky enough to have a working magazine, that would likely be worth a couple of hundred dollars all on it's own.
It's a relic, a small glimpse of history and a day long past.
In all practicality, it doesn't make sense to buy or own one for any real purpose other than collectability or "cool factor." Back in the day, it was the first. These days, there are many great options for a pistol in 10mm. I have two myself.