1)
Here it says 420 Kikar. In Divrei ha'Yamim II, 8:18 it says 450 Kikar!
1.
Rashi (10:14): The extra 30 were from Chiram's servants, who were with Shlomo's. They were part of the 120 Kikar that Chiram gave to Shlomo (verse 14). Divrei ha'Yamim does not mention the 120 Kikar.
2.
Radak: Of the 450, 30 covered expenses of the journey.
3.
Malbim: The 30 extra he gave to Cherem's servants, for their wage.
