I am interested in a self-driven punt - without a tour guide. I want to travel through the colleges. I imagine the trip will take an hour.
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I suspect all the commercial ones will be the same price - they always are in Oxford
However, almost all (all?) the colleges will have punts, either their own ones, or ones they've rented for the whole season. If you know someone from a college, and it's not too popular a day, they should be able to book a college one for free / cheap (depends on the college)
Otherwise, a few handy tips:
Scudamores is the usual choice. They have rental stations at both ends of the 'college backs' stretch of the river - Mill Lane or Quayside - as well as an location that lets you punt to Grantchester, but won't take you by the backs (Boatyard). Punts can't traverse between the two stretches (i.e. Scudamores won't let you do that - there are rollers that allow college and private punts to do it). Their current rates are 25 pounds an hour, with a discount if you pre-book an hour-and-a-half online. Be prepared for a wait in high season.
Trinity College also rents to the public, at 14 pounds per hour, with reduced rates for university members. I suspect that the wait will be significantly longer, but they are definitely the cheapest if you don't have a university association.