There are often WSOs on the Warrior Forum where writers offer to write salesletters for a few hundred dollars. Usually, without such discounts and special offers, you should expect to pay in the low thousands $1K-2K. Of course, there are always Warriors looking for writing assignments in the Warriors for Hire section that charge reasonable rates and usually do very good work. For expert copywriters such as Vin Montello or even Frank Kern, you're going to be paying much more than that.