Sounds a lot. but not looked at those particular cruises.
Looking at an equivilent trip this year to see what I could do it for booking today
I will pick the 7n 10oct-17Oct 2010 Jewel cruise ex NY
$549(inside) $879(balcony)
tax $129.76
$679 say £445
2011 Oct15 prices
NCL US cruise price $499(inside) $749(balcony)
Tax $137.44
Looking at Flights, say 9th and 20th OCt 2010
Virgin current sale £357
say £800 leaving around £450pp for 4 night hotels
Holiday inn(midtown/time square) with family and friends rate.
9th 1 night $270pn
17-20 3 nights $180pn
Say around $900 with tax and a taxi £588 so <£300pp.
I would focus on the hotels for reducing costs,
Flight hotel package through Virgin might work.
The above was a first stab without any searching just picked cruise flight hotel.
EDIT:
Just noticed there is sale on the Cruises for Nov that brings the cruise price down undr $399
I thnk if I was looking at next year I would pricup basedon booking in July(using todays prices for this year) and only book earlier if I could better these prices.