How much money do you have to giveaway for each level?

Happens any time multiple game listings are stored on the same store page, and a higher base value listing goes on sale lower than the page's default (ie, topmost) listing.
The Daedelic adventure games are the most noteworthy/common culprit, with their collections regularly going on sale lower than the base games do, thus causing the base games to report as having a base value of $50 or more (while the sale persists).

[Example, The Whispering World is currently reporting at $6.79, while the Adventure Bundle is reporting at $4.99- the store page would report the latter value for The Whispering World for this duration.]

When a game's default retail price drops (or, far less commonly, increases) that affects a similar (and likely more permanent) change to your sent values. Otherwise, things that adjust your sent values include games getting removed from the store (which often sets their reported value to $0), games going F2P (and thus also changing their value to $0), games getting retroactively added to the bundle list (or rarely, removed from it), or similar situations.