Hello Jonny, and welcome to the friendly Camera Labs forum!
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The Nikon D3100 is a very competent camera and if you get the 18-105/VR kit-lens you have a set that should produce many good images with no immediate need to add other lenses. If you're ineterested in understanding what lens(es) you need if you go for a trip to say Venice, have a look at my write-up here
: It's not so much you really need lens-wise. So plan to stick to your kit lens for a while!
As to prices: nobody can predict the future so the only thing I can say: be sure to get the presents for your loved ones before taking the plunge - and: good things come to those who can wait...
Thomas (beware: Nikon-fanboy and moderator!) My Lens Reviews
, My Pictures
, My Photography Blog