doubt about the value of a gift

normal

Normal unless the game has been bundled (or had more than -90% sale).

The full price....as long as it isn't in the bundle list. Or hasn't been placed in the list yet and is set to be.

Normal value, as long as it's not on this list (at which point you'll get 15% of the value)

If it doesn't appear on the bundle list it counts as the value of the normal full Steam price.
If it does, it counts as 15% of the normal full Steam price.
In general, if the game can be obtained for more than 90% off, even through other means than Steam, as long as it is redeemable on Steam, it might be retroactively added to the list and your value will be reduced to 15% of the normal full Steam price. Bundled games, unless they're on a high tier, will almost always be added to the list (retroactively).

sg uses USA store prices for cv.
anything over -95% will count as "bundled", which means it adds 15% of its value to your cv.
all regions are considered so games usually on -80% will be bundled because in RU they are super cheap.

Don't worry about the sale price, this website can't see how much we really paid for anything... :)

Also, if you're giving away cheap junk to get a higher level, you should probably follow everyone's suggestion and check the bundle list before you spend any money. You only get credit for 15% of the store price for anything in the bundle list. If you find something insanely cheap that's somehow not on the bundle list, don't be surprised if it appears later, effective retroactively.

p.s. Giving away cheap junk to get a higher level isn't much fun... If you give away a game the winner would enjoy playing, you would probably both enjoy it more... :)

p.p.s. Oh, unless the winner just wants to sell the trading cards, then it makes no difference... :(