Help Building Ben-Ben EDH

So my roommate challenged me to make a Ben-Ben EDH/Commander deck, and I'm starting the preliminary plan (http://deckbox.org/sets/478064). However, I'm having trouble solidifying my theme, and finding cards to help advance that theme. I'd love some help from those of you with a little more knowledge in this area. Some parameters:

1) My meta is pretty casual, but that doesn't mean I want the deck to suck. I occasionally play against some pretty intense decks, and I want to be able to keep pace, though I understand the theme doesn't lend itself to winning.
2) I build budget decks, so my total cost is usually under $200, and I don't generally like to purchase cards worth more than $15 unless they are extraordinarily good.
3) I want to actually use Ben-Ben. I don't want to just build a red deck with him there for color.

Thanks for any help you can offer!