Hi we did this trip last year too, wonderful city and the Ryanair-airport bus thing is so easy, only thing we found was that we got ripped off by a taxi from Termini stn to the hotel - the guy charged us E 25.00 after doing a couple of loops of the block, whereas return trip cost us E 8.00 but it was 1am on a Sat. so not then end of the world.
We stayed at Hotel Colosseum and it was dead handy, it's in a residental area there are 2 Irish pubs with PERFECT Guiness within a 5 / 10 minute walk and some really nice cheap restaurnants nearby too. It's basic, clean and reasonable.
Booked through Venere.com
Enjoy!
S