In Catania you can have an inexpensive but very good dinner with very large portions at VUCIATA KITCHEN MARKET, on Via Gisira, in the fish market area that turns into a restaurant zone at night. Lots of tourists go there but it's not at all what I would call a "touristy restaurant." Maybe hard to explain, but I've eaten there on a few recent visits to the city and been very happy. They are quick to pack up your leftovers so you can take them back to hotel for snacks, which many do since those portions are huge!! Their eggplant parm is memorable!!
Another very solid Catania restaurant for fish and seafood is LE TRE BOCCHI. I'm not sure if they speak English there but it's just fabulous..lively local scene, great food......just great.
The one now famous because Stanley Tucci featured it on his tv food series is this, and it's very good as well:
ME CUMPARI TURIDDU. The donkey meat (forget the name of the dish but its very popular in Catania and SE Sicily) is so sweet, but all the dishes are good there and its a pretty restaurant with very kind servers and staff.
In Ibla, in the low-ish price range, I'd highly recommend CANTUNERA IBLA. It's open only for lunch but their arancini is just wonderful, with some unusual flavor combinations. Closes at 3pm and one day of the week.