Not that long to be honest mate, is it flat or up/down hill much? Tho to be honest when walking or driving you dont notice as much as on a bike.

A while ago when all my cars were fucked I used to ride my bike to my Mrs's house 10miles a day every night (5miles each way), was up and down hills the whole way, nothing killer on foot, but riding a bike fast as fuck you sure noticed it.

used to take i dunno, half hour i think but riding fast (if its relativley flat you will be able to ride fast as fuck and no effort, but gradiants you feel much more than youd think and you will end up going slower for a bit), was fooked for 10mins once got there just because of the hills, but keeps you well fit, and like you said, costs fuck all.