Radak: It refers to "Hischaten", which is Makor (like an infinitive or gerund). The same applies to "Zos Ta'aseh Lach Azvech Es Hashem" (Yirmeyah 2:17).
2)
What is "Rash v'Nikleh"?
1.
Radak based on Targum Yonasan: Poor, and a commoner, who is not proper to marry the kings' daughter.
3)
How could David call himself poor?
1.
Radak: I cannot give a proper amount to be Mekadesh the king's daughter.
1
2.
Malbim (19): Even though Sha'ul promised great wealth to the one who will kill Galyus, David pardoned it to be Mekadesh Meirav.
2
z
This is like the opinion that his Kidushin of Meirav was valid. If not, his pardon was mistaken! Alternatively, David held that the Kidushin [and also his pardon] was valid, even though Sha'ul disagreed.
