Asking this question w/o any details is like asking how much will it cost me to buy a car in California?
Some things to think about:
A) How long are you going for (wkend, a week, 2wks, a week but flying in-between the wkends)
B) Where / To am I flying? Given you're in MS, it might be cheaper to drive to AL/TN and catch a flight...
C) Will you rent a car or will you catch a train once in ITL?
D) Where are you going to stay? Only one city/place or multi? Also, do you care about 1 start or 5 star hotel? Maybe a hostel?
Check out sidestep.com for flights. I did a quick search from Columbus, MS to Rome, IT using 6/10 - 6/18 and the cost of a flight alone was $1,450; however, flying from Birmingham, AL to Rome was $1,220.
Also, Hotels.com is a pretty decent site and they do offer one of the best prices. If you stay in hostel, it can be from 30 Euro's ($50) a night... Hotel will most likely run you around $90/night
Car rental is around 300 Euros/week (Hertz is among expensive ones)... where train ticket is sold by zones and time (duration). Most likely around $100 for the ticket (see http://www.italiarail.com/ I think you want Rome to Ancona).
So for a week + food (NOT CHEAP), you're looking approx $2,300.