Magento: Price issue on product detail page.

This depends on which one you want to keep. The price at the top of the page is generally displayed as part of the "product type data". Take a look at template/catalog/product/view/type/simple.phtml, where you should see $this->getPriceHtml($_product);.
The price at the bottom of the catalog page is a little more complicated. If you take a look at layout/catalog.xml, the price block (product.clone_prices) is added to the block product.info.options.wrapper.bottom, which is then added to product.info.container1 and product.info.container2. Depending on the product, one of these will be echoed on the page. You can, however, just remove the line for product.clone_prices and that should remove the price.

Also I've noticed this within catalog.xml file:

<block type="catalog/product_view" name="product.clone_prices" as="prices" template="catalog/product/view/price_clone.phtml"/>