How should I ship a computer?

Any tips on shipping a computer? I’ve got one I’m sending to some family in another state and I want to get it their safely.

I do not have the packing the PC came in, and the case is rather large, 21x10x22 (inches) and 25 lbs. The case is also fairly empty inside, quit a bit of open space.

I’d also like to avoid buying expensive packing.

The computer has:
2xDVD drives
1xFloppy drive
2xSATA HDD
1xMedium sized video card
1xStick of RAM
1xMedium sized heatsink. (Standard AMD Athlon XP size)

Estimated value: $800

Ideally I’d like to spend less than $30 on packing and shipping costs. FedEx estimate for the shipping is $18