I will give you my opinion first , but others are free to chime in with their opinions and experiences.
Grapes you buy in the Superstores are generally table grapes meant for eating. Many of them lack in flavor and other qualities needed for making a good wine with. The acids are too low, the pH too high and the sugars are generally not high enough. They seem sweet because the acid is too low. They also lack in enough tannins to make a good wine, especially the red ones. I would save my money on them. You would need about 60 pounds of grapes for a four gallon batch and that would cost more than a good kit. If you want to delve into making wine from grapes, try to get some in season from a vineyard or buy a bucket of juice from George or other supplier.