Discount Tire Company (tires.com) around $250 each at 18 x 7.5 +45 offset or 18 x 8.5 at +38 offset. I don't think I would put rims with +38 on my car especially if they're 8.5 wide. Imagines in Opal are sweet.
Don't know how to explain it in a technical fashion, but in simple terms, if you go with a high offset (+45), the wheel would be positioned closer to the inside of your wheel well to give you the "tucked-in" look, as opposed to a lower offset (+38), that would make your wheel stick outwards. This is of course considering that both wheels have identical widths.
offset is determined by laying the wheel face down. Now you measure the distance from the back of the hub area to the rear lip. in this case in MM. Check what the stock ones are and go from there. If i am wrong someone throw their 2 cents in.