You could investigate the various repositioning cruises that take place at various times of the year. Most are at season ends but not all are. For example, Grand Princess moves from the med (starting from Rome) to the UK on 10th June at which point the ship then does the Baltic run. It's a 15 night cruise and covers quite a few ports .
Any decent Travel Agent, & I suggest an independent TA not the high st mob, can put any package together, tell them your wishes & they will put some options together for you. Holidays don't have to come out of a brochure & a good TA can tailor your package to your budget far better than a 'take it or leave it' option offered by a cruise company. Why not try the Free phone number top right of this page? Regards.