You would be amazed the value in a Seabourn cruise...especially if you forego the UK travel agent and book with a US agent where the terms are generally more liberal and the stronger Pound gets you a good price.
Remember on Seabourn your drinks and gratuities are included in the price. For some that can cost more than the price of the cruise.
Of course the quality of the ships, service and cuisine also make Seabourn a great value when comparing to P&O.