Mostly it is individual models of the Rare ships that fetch the higher prices (my Enterprise set me back about $15.) Cases of boosters are usually the best bet if you want lots of ships and aren’t particular which side you get. That though leads to having everything from the set but one or two ships and hence the steep eBay prices.
Also the market is small so you have a lot of guys trying to get the same half dozenish models.
Singles off eBay or popularcollections dot com is the best bet if you know what fleet you want.