First thought was a E46 sedan. RWD might be the hardest part. When the car seat is rear facing a sedan would make life easier, after their forward facing it's a struggle but doable in a coupe.
Besides a BMW:
Cadillac CTS
Infiniti G35 Sedan/350z - Maybe Coupe?
GTO or G8 (might not be below $10k yet)
Most European manufactures
Mustangs
F-Bodies - tight fit but can be done
Can probably be found in Florida in decent shape - 1990-1995 Ford Thunderbird SC - I wouldn't be embarrassed driving people around in one, but that's me.
80's Celica or Supra
Did find this, it's FWD but would be fun
http://www.ebay.com/itm/181656232030?ssPageName=STRK:MEBIDX:IT&fromMakeTrack=true No Reserve Sho!