I'm in a similar boat: I'm headin' down to Pax Unplugged too, and would love the possibility of sharin' accommodations with fellow Doomtowners! Especially given that the goddarn fleabitten so-n-sos who run the whole shootin' match decided to host the inaugural Pax Unplugged the same weekend as the Philadelphia Marathon, an' so the hotel prices are spikin' faster than an Aetheric Shockwave Inducer on overload.
I'm told the 'unofficial HQ' for Pinebox Entertainment will be the Holiday Inn Express, Penn's Landing (http://www.hiepennslanding.com/). Unless you have a government or other discount, however, you're lookin' at $92.48 US a night for a double bed (half of $184.98 US for a river-view two-bed room. They sold out of non-river view rooms a couple days ago).
My brother was in Philadelphia a couple of years ago, and recommended the Apple Hostel (http://applehostels.com/). It is centrally located both to the Convention Centre and to the Holiday Inn, and has the advantage of being 'cheap and cheerful' (with large lockers for storing things securely). My cost for the bed in a four-man room, including the $3/night surcharge for not having an HI membership, averages $40.95/night. (There is a promotion whereby booking 3 nights including a Sunday = $20 room charge for the last night.)
Map of the route, for those lookin' at distance and so forth: http://mapq.st/2x0n7jW. A is the Convention Centre, B is the Apple Hostel, and C is the Holiday Inn Express. Essentially, the hostel is two blocks down from the other hotel, and otherwise on route to the Convention Centre.
I actually ended up calling Apple Hostels about an hour ago, to ask if 4 Doomtowners ended up each booking a room for a 4-man room, whether we'd get booked together in the same room? Mark confirmed he'd do his best to ensure this... but as I was busy trying to book, a claim-jumpin' varmint ended up bookin' a bed out from under me! So the upshot is that we should be able to end up in the same room, and if we get 6 total Doomtowners in on this, we could likely finangle a 6-bed room for the group.
To that end, I've got a line on a potential cowpoke by the name of David H. whose lookin' to see if he can swing the trip to Philly. If so, and with you and me as well, we could either fill the last 2 beds in the 4-man room (and induct a jogger into the cult of Doomtown!) or would be half-way to filling a semi-private "Doomtown Bunkhouse" 6-man room...