D2D is offering GTA4 complete for the PC for $9.95
I used coupon code 11AA4D15D9B23408ECC0 9FD04949F395 for an extra $1.50 off
... but I'm not sure if its only for first time buyers. Give it a shot
though.
Link: http://www.direct2drive.com/9976/product/Buy-Grand-Theft-Auto-I