It is more like payments to be on the ends of the shelf etc.
If you don't pay your product will only be seen by people that are looking for it.
One reason the Tesco store is now so empty, is that they have made the delivery service so cheap. Salisbury are hitting the same problems of people not going to big stores as often.
As to prices, it depends on what you buy and how well you understand all the offers. E.g. some items are best when brought on 2 for 1 and then stored, knowing they will be on offer again within 6 months. (Or use CostCo to avoid paying the games.)