As I see it:
1) $28 seems pretty reasonable (I live in London and relatively cheap gym member ship costs £65 a month on an annual contract!)
2) 5-10 mins isn't far to go
3) You seem to have time to make it to the gym 2 or 3 times a week if you want to e.g. one day of the weekend and once or twice just before lunch during the week
I would keep the membership. Remember, you only have to work out for 45-60 mins a session.