Great post!
I'm Italian and I would like to advice you that actually Rome is pretty expensive. You will discover that we have several cheap plates that are really expensive elsewhere.
Pizza is REALLY cheap. If you go to Naples, you'll find the MOST EXPENSIVE pizzas at about 6 or 7€.
Pizza prices in Rome is okay and it's not strange to see a 4€ margherita pizza. And, plus, I don't think the pizza you took is good (just looking at the borders).
Seafood is really expensive, so I'm glad you didn't spend your entire salary. The name for that plate is "Spaghetti con cozze e pomodori". "Cozze" is the name for the seafood inside, "Spaghetti" is the type of pasta (probably it's "linguine spaghetti"), and "pomodori" is tomatoes. Hope that helps!
Even, "Pasta Bolognese" is not thy "typical" italian pasta. We like it, but it's not like our main dish. It's the easiest one, so we just eat it when we have no time, but we actually do even some more complex pastas :)
Thank you so much for your "rome-expert" comment, there are just so many things i need to learn about this city, I dont think the pizza is good either, but its okay to taste ^^