how long is a piece of string?!??!?!
the copy, photos & advertising methods you use to sell your members area content in your tour is more important than what the site looks like, and as a designer that hurts to say
if you aren't very good at design, stick with a really simple page layout and lots of thumbnails with really good captions & lots of 'join now because ...' links throughout the page.
this is pretty ugly imo, but it sells well & its really simple to build - just a few table rows of pictures that are the same size ...
http://www.amateurnudies.com/tour.html
my suggestion would be to have a go yourself, send some traffic, change a few things, send some more traffic, and if you still can't get a few sales, maybe have a designer look at it. At least then you know what to ask for.
imo the most important thing you can do is make your site different to everyone else's standard porn site tour ... very few designers seem to know what they are selling well enough to think as they design, therefore you get a template copy of the same site they sold a week ago.
Feel free to post your design as you go and i'm sure there are plenty of people who can offer you advice on what to do differently ;-)