$520.00
The standard tanks when combined with the speed an on-airport bias of the 650 design work well enough for most people. For myself though, more is better. I’d always get the long-range tanks.
Also, when combined with either of the Viking FWF kits – you will also get another 6L of useable fuel with the included small header tank.
All up, your new fuel capacity will go from 90 liters (standard; without the Viking FWF) to 118 liters (including the header tank). The extra 28 liters is pretty close to an extra 1.5 hours of flight time.
This kit option increases the size of the standard fuel tanks to approximately 15 U.S. Gallons (56 liters) per side, replacing the standard 12 U.S. Gallons (45 liters) fuel tanks (per side) – 112 Liters in total.
The price is the additional cost for a pair of welded aluminum wing tanks.