I have this happening too, but with just one item that i've found so far. The price shows fine for me on the category page, but on the product page says "$NaN (USD)". You can still add it to the cart and it works...but this is just odd. I came on to the forums here to see if anybody else ran into this while I look for a solution myself. nopCommerce v 1.80.
If anybody has anything I would appreciate it.
Editing to add links:
Category Page: http://blowsion.com/category/49-accessories.aspx?pageindex=2 Handle Bar Clamps Product Page: http://blowsion.com/products/714-handle-bar-clamps.aspx