Ego,
I'll tell you what. TWO of my best friends are in the UPenn postbac program and I've been to visit them atleast 3 times.
They aren't in the Special Sciences program, and instead, are in the postbac program in which you take upper level courses.
In the first place, Philly is a dump. Sorry to say, to all you fans out there, but the city is dirty and other than the UPenn campus, it's not very bumpin. Apt's and living is also quit expensive...anywhere from about $600 (which is rare) to about $1000 (which is the norm), and above, per month for an apt.
The postbac program (in which you take upper level courses) also seems disorganized and there is little support from advisors. From what I've heard, atleast 5 of the people in the program that I know (2 of my friends, and 3 of their friends), they all hate it.
Classes are about $1500 per class and you take them at night...I guess the cost/tuition isn't that bad, but the cost of living is high.
I'd check out some other structured programs. Or if anything, if your GPA isn't TOO low (like....if it's hovering at about a 3.4 or something), maybe just staying in undergrad for an extra year and taking courses would be beneficial. If anything, an MS would be helpful too (hell...you can probably get an assistanship, research experience, a TA position, tuition paid, and get some money at it all at the same time!).
For sure, you can get into the Penn program. One of my friend's had a 2.9 science and a 3.2 cum, with a 26 MCAT, and he got it. They are not very selective, and I'm pretty sure about that.
But, I'd advise against it because of the experiences of my friends. I'll give you their emails if you want em. Just PM me.
Good luck