No one has replied, because that is a loaded question. If you have a big bucket of money, pretty easy. Find a reputable shop give them your car and the money and come back in a year. If you are talking about doing it yourself you need to describe your skills before a prediction can be made on how hard it would be. You need fabrication skills, welding, sheet metal bending, machining skills and a huge amount of tools. Room to work and lay out. Still going to need a bucket of money. There are several builds on this forum. A supercharged Toyota swap and a Vtech swap. Both took over a year by people with mad skills and tools. It's hard and time consuming. Mounts, suspension, enclosure, shift linkage and exhaust need too be fabricated. Controls and wiring will be a huge under taking. You need all the wiring, computer and sensors for the Cobalt along with transmission and it's related hardware/software. The smart's wiring needs to be parsed and the essentials pulled out for lights and little else. You might be better off going with a custom harness and all after market gauges (big $). Because the smarts systems are all tied together, it's hard to retain many stock items. Short answer-very hard.
By the time you get this project done, you will have spent enough money and time on it to pay for buying a car with a larger motor and more suitable for racing, or whatever you want to do. Since a smart is a low production vehicle, and not easily modified for higher performance, aftermarket products will be scarce unless you have the equipment, technology and time to design what you need. And don't forget that big old bucket of money too!
You might want to check into a kit car where you can have a light body and use any motor you desire. Then you can have a car similar to a smart with an Olds 455 in it, with a supercharger, nitrous and a trailer hitch for hauling gas and tires.