Expensive yes but I will have a car (don't say ditch the car and take a train). So, any suggestions to avoid €25 a day?
According to parkopedia, 10 Euro/day at Piazzale di Sosta ("when ships are operating"). outdoor with video surveilance.
http://www.parkopedia.it/parcheggi/venezia/
Just be careful driving across the causeway into the city. They have RadarCameras taking your picture.
They've built huge, modern parking garages over in Venice in recent years.
From experience, used several times, there is a park silo (multi story car park - about 15 stories high) on Mestre, just across from the Mestre train station entrance which I have found to be safe and significantly cheaper than the Tronchetto / P. Roma options. Disclaimer - haven't parked there for 2 years because we have trained in the last several trips to Venice.
Stay in Mestre and find a hotel that provides cheaper parking. I stayed in the Hotel Kappa many years ago because I, too, brought a car. The hotel had a gated parking area for about 3 cars which they charged extra for. We walked down the block and caught the public bus to Piazzale Roma and from there you're in Venice. It was an awful experience. I would never again take a car and never again stay in Mestre. Since you don't want to pay 25E per day parking, and you don't want to hear people tell you the obvious (ditch the car and take a train) - then look at Mestre. But it won't be the "Venice Experience" you're looking for.