The Sprinter chassis cost difference can buy a lot of fuel, although Sprinters do hold their resale value extremely well.
There are some tradeoffs. You are going to pay Mercedes prices for maintaining the vehicle, however Sprinters seem to be reliable, otherwise one would read tons of threads complaining about it here, or on the Sprinter (sprinter-source.com) website.
Of course, if you can keep your rig for one or two more years, the motorhome industry is going to go through some gigantic changes, arguably some of the biggest since in decades, due to the chassis change (Econoline to Transit.)