The filler hose for a 7' bed is about 2" longer than one for a 6' bed.
The price difference is likely due to demand... I would guess there were probably 10 six-foot bed trucks sold for every one seven-foot bed.
FWIW, you also do get what you pay for... The cheapest hoses have an unreinforced, very dry-rot-prone outer hose. Dunno where you're at (your location isn't in your profile), but here in So. California they last maybe 1-2 years at best before cracking again.
There are a couple workarounds for the thrifty among us though:
Cut the outer hose in the middle and insert a 5" length of 1½" galvanized water pipe to lengthen it (secure with hose clamps, the inner hose should still just reach w/o cutting), then fully wrap the outer hose with a good quality electrical tape (such as Scotch "Super-88") or other covering that will prevent air pollutants (ozone, smog, etc.) from being in contact with the rubber of the hose (the hose I modified to fit my BII has held up going on 6 years now with the Super-88 tape on it).
Hope that helps... Welcome to TRS.