TrailerSaver 3rd air bag

I purchased my TrailerSaver hitch used. I've noticed on forums and pictures that some other people's TrailerSaver hitches have a 3rd air bag that allows up to 7500 lbs of pin weight. I don't plan on hauling a trailer that heavy, but I'd like my hitch to be all it could be. I looked at the kit from Hensley. $500!!!! Holy cow. I looked into cobbling my own kit. It wasn't hard to find the air bag (air spring) that was used...Goodyear 1BB-564. It cost me around $80. I found a couple pictues of the actual Hensley bracket and thought about fabricating my own. I had been happily surprised to purchase the Hensley shock kit direct from Hensley for only $99 plus shipping. I decided to email them and see if I could purchase just the bracket I needed. I did, and about fell over when they said the bracket was only $25 plus shipping. So...why do they charge so much for the kit? Here are the two ingredients needed to add the third airbag to the hitch. The bag uses normal 3/8"-16 bolts. My invoice with the bracket part number. My HDT homepage