It´s not neccessarily going cheap. Sometimes it is possible to get the items assembled in the kit for a better price. When buying in bulk (e. g. for assembling several FAKs) the price can be significantly better.
In some cases buying the kit can be the better choice. In Germany it is required to have a standardized FAK (DIN 13164) in the vehicle. Typically the kit can be bought around 9€. The items in the kit usually are of good quality. I recently ditch my vehicle kit as the sterile items expired. The adhesives where still good despite of sitting in the car for 5 years.