My kneejerk reaction was reg fee, but godaddy is showing that leadgen is taken in all the major extension including .mobi and .us. Google keyword tool is showing 2,400 searches a month for the US market on average. Also, ileadgen and myleadgen are taken.
Based on the above, I would say low to mid xx to a reseller, maybe more. I don't know enough about the industry to guess at an end user price.