I did not bother to check the price, but any DIY person can put together the same type of a system.  A couple of tips for DIYers
- Buy as much battery capacity as you can afford.  If you have the space, lead-acid batteries will save you a LOT of money. 
 LiIon weight less, take less space and last longer IF you have a large wallet !
- You ABSOLUTELY need a DC-DC charging solution so that the house batteries get properly recharged while driving
- Find an inverter/charger/automatic transfer switch like theses from Samlex
I really like the Samlex unit because all connections are made in one place.  Another bonus with the Samlex inverter/charger/automatic transfer switch is that it is setup so you can easily add generator 
(with optional auto-start) and solar !