Ebay, indeed. You might even be able to buy mine ('skins), but they're likely to be pretty pricey...
I've been auctioning my 'skins Season Tix on ebay for about 5 Years now, and have a pretty good handle on what mine will go for, at least. Lower Bowl, inside the 1st 20 Rows, almost midfield (they're sweet seats). Face Value for the set (4 Tix & Parking Pass) is $435 for a Game, and I can usually get that for the 'basic' Games no matter how the Season is going, mostly due to the location. Eagles and Giants usually sell for about twice face value, and Cowboys for about 3X Face Value. Night Games add anywhere from 10-50% above that, depending on the situation involving the 'skins and the Opponent. Given that it's a rivalry Game vs a Divisional Foe and bitter rival from right up the road, and I'd estimate that Eagles/'skins will draw a top bid of about $1000 (for my set).
That being said, there's no doubt you'll be able to get Tickets, and if the 'skins are treading water or already in the tank, which they likely will be AGAIN, and you should be able to get 'average' seats for right around face, which will probably cost around $50-$75 per.
Good Luck, and feel free to contact me as the date draws near...I have some connections with the Team, and you just never know...