The reason for the price difference is the quality of the materials internal of the converter. Some aftermarket stores sell "universal" converters which aren't really made to faqctory OEM specs. These converters generally do not last as long, and in some cases do not work well enough to satisfy OEM needs. Unfortunately, your best bet is going to be to get as close to OEM specs as you can to avoid having to replace the converter again in just a short period of time. Like the old saying goes: You get what you pay for.