Benelli stopped importing mag extenders to the US, awhile back. It's not a BATF ban, but a decision by Benelli, so I understand.
Anyway, I see where Benelli mag extenders are going for between $300 and $400 on Ebay! Not too long ago, they were retailing for $65.
Tom Knapp is offering new 2- and 4-shot mag extenders from his web store at about $90. Still quite a mark-up, but nothing like what they are selling for on Ebay.
I was just shocked at how much they've gone up. I could sell mine and buy a whole new gun! Wait a little longer, and I could probably get a Vang Comp just by selling my mag extender...