I was going to suggest the partial plan as well, plenty of good seats in and around sections 205 and 225. If they want to attend 9-10 games, pick a 20 game plan and StubHub the extras. Finding a full season group would probably be a bit cheaper, but the added flexibility of picking games and the STH perks would make it worth the slight extra cost.
I had seats in 313 in 2008 and 2009 but I would pay $5 more to sit lower in the mezzanine.
I'm worried whether I would actually get anything close to season ticket price on Stubbub for mezzanine seats. Anybody with any experience? Plus, the thought of unwittingly selling to Philthies fans is disturbing. But I agree it could be hard to find a season ticket group in the mezzanine.