Venice

The historical center of Venice is small enough. You don’t need to limit yourself to San Marco, which is the most crowded and most expensive Sestiere (district), especially near Piazza San Marco.

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*What's reasonably priced, preferably in euros? Reasonable to you may be expensive to me or vice versa.
*How many people are traveling with you? Do you need a single room, double or more?
*Do you have any physical limitations? To reach most hotels you will walk over canal bridges. Some "reasonable" hotels may have stairs.
Without more information it's difficult to answer your question.

More information would certainly be helpful. Specifically: dates, number of people, and price range in $ or €. Have a look on booking.com, and use their filters to refine your search. Having said all that, we've stayed 3 times at Hotel Campiello. It's 100 m from the San Zaccharia vaporetto stop and 200 m from P. San Marco. On a very quiet side street, and decent restaurants close by.

This similar question today
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Hi Pam,
We've used a RS guidebook recommendation, Hotel Campiello, twice. It is pretty close to St. Marks Square and at the end of the vaporetto line (San Zaccharia). I would stay there again...convenient, pretty, and a great breakfast. Enjoy!

We've stayed at the RS recommended BandB B&B Corte Campana several times. https://www.cortecampana.com
It's near San Mark's, well under your budget and we love it. The BnB experience is somewhat different to the hotel experience but we really like it.

I love Vencie, have a great time,
=Tod

Our RS tour stayed at Hotel Mercurio, about 1/2 block from the La Fenice Theater. I have no idea what it costs.

We stayed at Hotel Concordia which is just left of St. Mark’s basilica if you are looking straight on.
Lovely hotel. FYI, the entrance is on the backside of the square.
We were there this past September.

Hotel Al Codega is nice. It's right between St. Mark's and the Rialto Bridge (about 5 minutes from either one). The hotel staff was nice, breakfast was great and there is a small canal just steps away where the water taxi picked us up and dropped us off when we needed it.

Since you haven’t come back to answer questions or said when, I’ll throw spaghetti on the wall and second hiredman’s B&B Corte Campana recommendation. I’m staying there for the second time in August.