As far as entrance fees are concerned, if you budget 10 euros a sight, you will be okay. Some are more, most are less. Just figure out what you want to see and budget accordingly. Most sights in Rome are free. However, some things do require a fee. All museums, the colosseum, baths of caracalla, and the Borghese gallery all require a fee.
Souveniers are trickier. Rome is not a terribly expensive souvenier city. You can get some bargains. If you are looking for clothing, you can usually find the same thing for less back in the states. Same thing with good quality leather. Buy it before you go or after you get back. Any other type of souveniers, bargain for. Offer a reasonable price and you should be able to get it.If you want to take a day trip to Pompeii, the train will cost between 17 and 23 euros for a second class ticket each way. The circumvesuviana train is less than 5 euros. The entrance to pompeii is about 12 euros. You can buy food on the train or at the station outside of the ruins for a few euros. This is an all day trip, so bring some extra cash. You might want to do a guided tour of the site. ( not sure of the price for this but I would budget about 25 euros).
You can do Rome for 50 or less per day and have a great time or you can spend more and have a great time. I guess it all depends on where your comfort level is.

