Looking more like a trade off. Sorry to hear man!
Sometimes you have to make the hard choice to be stangless for a period of time, atleast until you can be in a more financially secure situation. Buy something cheap and economical and you will enjoy the maintenance free/worry free driving at the cost of your commuter being soulless. Find a good deal so you won't be upside down again and look to the future goal of having another mustang when it can be what you want and practical financially.
Seems to me you cant afford the mustang you want, but still need to ditch your current money pit car. I'd list on craigslist and see if you can find the right buyer or trade it in, but on something economical.
Dump the car, pay rest of loan off, buy a garage, pay that loan off, have another kid, pay that loan off, buy a mini van, dream about your old mustang that you could still have, pay mini van loan off....buy another soccer transporter....and so on. Is another mustang in your sites? If your like me, the last kid will have to be 18+ before ill even be able to look at what I want.