Well, as I said, it is very expensive to eat in Venice - for a multitude of reasons (and if you're not a local!). There are some very good places and a lot of mediocre ones (not bad, just mediocre).
You are right - Fiaschetteria Toscana is in the top tier of cost (and quality, IMO). Sorry, I thought I mentioned that it was more expensive, but see that I didn't, after re-reading my post. Our party of 8 loved it for a festive birthday celebration and the food was extraordinary. Perhaps we were given extra care because a friend of the owner called in advance for us.
While it's possible to run up a big bill when eating anywhere in Venice, I certainly don't consider Santa Marina or Corte Sconta to be among the most expensive in town. For example, Al Covo is still recommended as inexpensive, but when I tried it several months ago, it was around 100-Euros a person. At Santa Marina a few months ago, I ordered their tasting menu (7 courses, I believe), wonderful food, and I think the menu price was around 70Euro. After inhaling a mussel broth filled with sea bass ravioli (1st course), I decided I better pace myself and finished about half of the remaining courses. They discounted my bill 30% - I had heard stories about this, but thought it was just hype. Amazing!
Corte Sconta, I think, does become more uneven during the height of the tourist season. Definitely more crowded with tourists and service can be curt. It seemed the OP would be travelling relatively soon and my experience during off-season was very good.
As far as restaurants & tourists in general - like it or not, Venice IS all about tourists. The locals that still live on the island are a small minority now and, given the cost of everything on the island, can't afford to eat out ever night as the thousands of tourists do by necessity, even with their local "Venetian's discount".
For less expensive, what about Osteria Vecio Fritolin for fritto mista? Or good thin crust pizza at Pizza Al Volo? There is a tiny family restaurant around the corner from the Danieli that is very good and reasonably priced. I'll try to find their card and post the name.