Botenverhuur de Rijnstroom, Weg naar Rhijnauwen 2, has everything from one-person canoes for €4 for one hour, up to motorboats that you can rent for the whole day for €60, with everything in between. They're located between the Utrecht stadium and University de Uithof and have routes that take you through the old city center or out into wilder, greener locations.
If you want a party boat with food and drink, you may want to consider the tapas boats that sail through Utrecht. Besides the tapas boat, they also offer BBQ, high tea, stamppot and lunch boats. They're good for large groups, seating at least 10 people, which means the price is much lower if everyone is chipping in. If you want just a boat and skipper, that goes for around €140, with the food and drink boats going up in cost from there.
