My husband and I are celebrating our 35th wedding anniversary...and have also been looking at longer cruises. The 7-10day just don't do it anymore. Having said that...I must admit that your budget may be a bit of a problem as it was for us.
Princess has a nice cruise leaving in November 2012...for 15 days out of San Francisco for a balcony it will fit your budget if you catch the sale. (we booked a mini-suite at a super GREAT price!) The cruise is round trip from San Francisco to the Hawaiian Islands. Lots of sea days too of course...but then you get to cruise the Hawaiian Islands..how great is that?
Celebrity and HAL are excellent cruise lines but the cost will be higher than Princess...(from our research) for Hawaii..and they leave from L.A or San Diego...
There are Panama cruises that will fit nicely into your budget offered by all three cruise lines and they still have cabins open with balconies...again the prices NOW are outstanding.
Alaska is going to be your most expensive cruise and none of the cruise lines offer more than a 10-14 day cruise only. There are Cruisetours (cruise & land tours combined) that may be longer...but you will have to compare those with your current budget. (HAL & Celebrity offer them)
We're only familiar with west coast boarding...so can't suggest ships leaving from any ports than the unusual we know...San Francisco, Long Beach, San Diego..Seattle Washington and Vancouver Canada...
The time to book is now when the cruise lines (especially Princess) are having their sale..at least that is our experience. We've been looking for about 3 weeks for just the right price...and finally booked yesterday because the price was outstanding!