First, welcome to the forum. Second you must understand the different versions of the car. There is the "base model", then the "limited" models, then the "SRT". They will all look very similar on the outside. The SRT's can usually be easy identified as the rear wings are way different than the base or limited models. Also they have different wheels (unless they have been replaced).
Also a roadster (convertible) will usually cost a little more than a coup. Of course none of this is set in stone but a base coup would go for under $5000. A limited coup runs about $5000-8000. A limited roadster runs about $5000-12000. A SRT will run about $10,000-18,000. Of course condition and miles have a lot to say when figuring out its value. If you find something you like take lots of photos and post questions about it here. You will get honest help.