The first generation had engine options ranging from a 110 hp Sirius I4 up to a Mitsubishi V6 6G72. The GL was the bottom trim, with the GLS being the upgrade with the more powerful engine.
The second generation tried to mimic the luxury car makers such as Mercedes Benz and Jaguar on the outside, but it was still a Hyunai on the inside and under the hood. The top engine once again was a V6 from Mitsubishi making on 142 horsepower.
The third generation started out looking like a Ford Taurus, but a redesign in 2000 made it look more like the German luxury cars that Hyundai's designers were trying to imitate. A 170 horsepower Delta V6 was now the top engine, and sales surged in the U.S. in large part due to a 10 year manufacturer's warranty.
The fourth generation Sonata looks more like a Honda Civic than a German luxury car, but its performance is way up over previous generations. It does 0-60mph in 6.6 seconds, and its top speed is reported to be around 147 mph. A speed limited will likely be used on future Sonatas with V6 engines. The upscale model with the V6 retails for $24,500, making it a steal for families who want a car with some kick.
These cars are all over the used car market. There's a guy near me who only sells used Hyundai's. The new Hyundais are flooding the market, making the used ones less valuable and cheaper to pick up. I suggest looking on eBay, where there are always deep discounts on non-collectible used cars and plenty of parts to boot.