Here are some hotels that I came across while researching where we want to stay in Rome. April is not the most expensive season in Rome but it is not far behind, and the 4* hotel that was recommended to us was priced at 159 euro/nt. We considered 3* hotels and vacation rentals that could keep the cost down a bit, but it had to be somewhere near the historical centre of the city.
Hotel Napoleon - 4* near Termini w/ big breakfast
Hotel Caravaggio - 3* central hotel
Hotel Romae - 3* near Termini
Hotel Elysè - 3* near Termini
Vacation Rentals
Leisure in Rome - Apartment rentals
Frommers Forum - other ideas for places to stay in Rome
Venere.com and Booking.com are two big sites for comparing prices on European hotels.