Now I'm no slouch with it comes to my love for all things Sharpie related, but paying over $10 for one black and one red Sharpie seems like overkill (especially considering I usually lose them) in this day and age. RStevens doesn't even pretend that these are something special, he just knows there are always going to be a fair number of people interested in purchasing them just for the novelty.
Your standard black Sharpie runs about 60 cents, but you can probably do even better if you find a coupon or a sale. If you look to buy the blister packaged 5-pack of black Sharpies you'll end up paying more, so just buy them individually. Your standard red Sharpie runs about 70 cents (I couldn't tell you why it's more expensive), and Sanford doesn't offer them in the more expensive blister pack, so you can save yourself the simple division.
If you are looking for a Sharpie that will make your friends green with envy, you could pick up a Marker of the Beast pack (and don't forget the shirt) or you could get one the Special Stainless Steel Sharpies. They will easily out last a standard Sharpie in durability and the replaceable refill cartridge means you'll never have to throw it out.