( 1)Y = 120 X+80(30-X)= 40X+2400

∫(30-X)/3≤X≤2(30-X)/3

∴8≤X≤ 12, and x is an integer.

(2)∵Y=40X+2400 increases with the increase of x.

When x is the smallest, that is, X=8, ∴ Y is the smallest.

8 basketballs and 22 volleyballs cost the least. At this time, it needs 2720 yuan.