Your site looks great. Very clean. What are you trying to customize? Have you tried Nvu? there is a template extension for it called mambo template builder, or template bulider for Deramweaver.
Do you know how to work with css? A good place to start is at w3.org they make the standards, or do you just want someone to do it for you? If you want someone to do it for you please just ask and offer frih$. There are alot of people in this forum that realy like to do it.
There are many free templates available probably the bigest collection is at joomlaos.de around 1300 templates.