Hello and welcome to the forum.
Condolences; this is not what you were expecting from an impeccably maintained car and I can understand your feeling bereft.
Most of us here are from Europe, so we're not familiar with the intricacies of either the car or the way the automobile market works in the USA, but I'd expect your options to be broadly similar.
Firstly, you've been unlucky; it's most unusual to need to replace an engine within the service life of a modern car, and the 500 is no different in this respect.
A new or factory reconditioned engine is likely to be expensive, possibly too expensive to justify putting into an 8 yr old car. However, there is generally a plentiful supply of used engines available from breakers for much more reasonable prices. Obviously if you can't replace it yourself, you need to find a service facility which can. The biggest problem in the USA is probably finding an independent garage sufficiently familiar with the car to take this on; it's relatively delicate work in a very confined space; this is very different from dropping a V8 into a more typical US car.
You've a number of options. If you have the skill, tools and facilitites to swap an engine, then sourcing a secondhand engine and fitting it yourself is probably the best one. If you haven't, then give serious thought to selling or trading the car 'as is'; this cuts your losses and passes this and whatever future problems there may be onto someone else; you can then buy another car and move on.
Taking it to a Fiat authorised dealer and having them fit a new engine will get you peace of mind and a warranty, but could easily cost significantly more than the market value of the car.
Getting it fixed by an independent repair facility will be cheaper, but if it doesn't work out, you've put more money into the car and will still be left with a problem.
In the UK, you might make more money by breaking the car and selling the parts than it was worth in the first place. @
typecastboy, what would you do in this situation?
If you do keep the car, it's important to find out
why the engine failed; if there's another underlying cause (coolant loss being the most likely), then this also needs to be dealt with, or any replacement engine will soon go the same way.