The human brain tends to rely heavily on the first number they encounter. This is called anchoring.
In layman’s terms, this is the fact you will use the first number as a reference point.
When selling you can use this to your advantage: simply start with your most expensive bundle. Then offer alternatives with less items and hence cheaper.
All prices will be compared to the first price in the customer’s brain and as such will appear to be bargains.
You can consider this to be upselling in reverse: sell more by selling less!