Rent a car in Venice will not be necessary, that is, you do not have to solve the problem of how to rent a car in Venice cheap or without a deposit. This is a unique city in terms of transport infrastructure, where there are no roads or bikeways. Only water transport.
So if you have arranged a cheap car rental somewhere in Italy or come to Venice by your own car, you have only one thing to do - to park it nearby. For example, on the island of Tronchetto, in Piazzale Roma or in the local "staging post" - in Mestre.