A couple of other places not already mentioned:
There's this growing chain of Mexican places around town, justly famous for their home-made tortillas, perhaps you've heard of it, La Quebrada. They have a plainish shrimp ceviche. What's much more gusty, is a fish ceviche "Acupulco style" in a bracing lime bath. I ask for extra jalepeno's and it is about the most perfect cup of ceviche I have found around town. Various locations including one now next to Steve's Shish Kebab House on W. 63rd street, how many people get to have 2 of their absolute fav. places next to each other?
Frontera and all the Geno Bahena places serve the same marlin ceviche. Or would it be more accurate to say that Bahena continues to serve the ceviche he learned from Frontera. I think of this ceviche as safe if you know what I mean, but it's good too, and something I nearly always order at those places.
Mi Familia (3624 W. Fullerton) is a small, hardly discovered Peruvian place in Logan Square. What makes their ceviche special is not the abundance of canned sea creatures but the searingly hot (insist) blend of peppers that support the dish. The restaurant owner will actually have you eating the pepper mix on crackers without the fish, and here's a dirty little secret, it's a lot better that way.
I know you want not fancy, but the yellow tail sashimi ceviche at Sushi Samba Rio is like butter (I mean like spicy butter). Get an order at the bar. Walk out. You'll have not spent more than some of the other places mentioned.
Rob