You could do it for about 45€ at a pleasant restaurant; especially since you won't be ordering wine. If you go to a more touristy restaurant, you will pay the higher price of course.
For me, I enjoy Pinot Grigio, so I would order one glass with my dinner. It was 5€, but I enjoyed it, and they weren't skimpy with the wine. I would think a pasta dish or pizza would be inexpensive compared to the second course -- meat or fish and vegetables. But, I guess it depends on the restaurant.
Some restaurants charge for bread. If you and your wife are not bread eaters, then perhaps tell the waitstaff ahead of time as you sit down. It's usually about 1,30€ to 1,50€ for most average restaurants.
Most evenings, I ate at my local restaurant which is close to Termini. But, the location may not work for some travelers.
As I walked through Campo de' Fiori and Piazza Navona a few times, the restaurants seemed full, but the outside tables appeared to be seated with travelers.
There is Ristorante Campo de' Fiori on via della Corda, 3 http://www.campodefioriristorante.it/ right near the market area down a little alley, very, very good with reasonable prices. Check out their menu.
If you pay by credit card, just make sure to pay the amount in euro and not the DCC.