Nate, as Gonz has mentioned some details about your locality would help.
In Australia the Elantras come with 1.8ltr engines and there is nothing in the way of engine upgrades that I know of as all the performance stuff is engineered in Korea for the 1.6 and 2.0ltr engines.
About the most you would be able to do is a custom air intake that you would have to make yourself though that will add only small changes in the way of performance and a custom cat back exhaust system as there is no extractors made for the 1.8ltr that I've seen so if you want them they would need to be custom made and wont be cheap (extractors will void your engine warranty), one of the Sprint car shops I've dealt with before quoted about 2k to custom make extractors but luckily they make them in Korea for my 1.6ltr.
ECU upgrades are pretty much non existent unless you're able to find someone very capable of doing an ECU out upgrade but I've not seen/heard of anything for the 1.8ltr's, there is some new Haltec ECU replacement options coming onto the market though quite time consuming and costly at around 3k and really only of benefit if you've already done the intake and exhaust first.
