We done venice and rome stayed venice 2 nights(was just outside venice but bus right over to it in ten mins from outside hotel) then train to rome for 2 days again not center of rome outskirts but the metro is so cheap and frequent it's easy to do and very easy to work out and use, , we booked thro ViVa holidays and were around £500 but that was a few yrs ago we got the passes for attractions online so was cheaper than paying individual it's the Roma pass also got them for venice it can be done on a budget u just have to do a bit of looking around and use bus, trains for transfers instead of booking thro agent travel in Europe is much better than here we had decant hotels but as I said outskirts rather than centre do some digging if u really want to go it can be done.