^^^Tim I'm pretty sure he was talking about the old body fusion's as you won't find a 2010+ Fusion for $300/month, and the old style did suck in backseat room...and all around.
I would know, I had a 2009...I sold it pretty quickly.
If you want to keep it under $300/month, I'd assume you're thinking about spending $15k overall if you plan on a 60month car loan. That's how I'd look at it, like stated above, a total value rather than a monthly commitment. Because $300/month for 36 months is a lot different than $300/month for 72 months.
For $15k I'd consider a Mazda6, like 08 and prior, v6/6spd auto, etc, and can do 3 adults in the back, and is peppy/fun to drive. That's probably the newest/nicest car you'd get for the money. If I wasn't worried about some miles I'd definitely look for a CTS-V, 2005ish Nissan Maxima, etc, but realistically how much backseat room do you want/need? A 4door won't ever be as nice/big as an suv/van.