If you are on a tight budget then I would certainly suggest that you DIY trips. If you check back through the previous answers (Selectively choosing port names in the "Search" section) you will find all of the answers you need. All your ports are easy to DIY. You can get further information from the tourist site on the net for each of them and further info from "Tripadvisor", "Virtualtourist" and I know Albert will recommend "board cruise critic". Once you've done it on your own or with fellow passengers you won't stop.....regards Neil Dow.
Ha Ha - am I that predictable!?
As the previous passenger said DIY are best, but you must be informed, read old and new reviews. Ross put one on with fantastic detail and we did this trip too. Barcelona get on the bus with an all day ticket, But walk up les rambles and get the bus at the top, as traffic is bad and you waste half your time just getting to that bit at the top where they all connect when you could have walked it in 10 mins. Take your time and acrew as much info prior to setting off and take advice. We love DIY trips, last year we had an old couple come and find us every night to ask about our adventures of that day. They had spent a fortune on trips. However there may be some places that you may need an organised trip. I have only been on 5 cruises and they have been around the Med and Norway. happy hols.