Some of the themes shown in the demo are quite nice, but I was wondering what it take to have the gallery fully integrated into my site skin using the customised graphics etc, or what would it cost to have an expert do this for me?
That really depends on what your site looks like.
It is possible to edit any of the themes to look different, and it should be possible to create a custom theme that matches.
Without seeing your site, it's impossible to say for sure how hard it would be.
You can always post a request on the freelance board, where you can ask for paid help.
Thanks Casper, I have put a request in the freelance area as you suggested.