Hi,
"These rims only come with the original center caps designed for the Passat 35i. I also had those on my GTI. At least they properly cover the hub and bolts. However, you have to be careful, as 4-hole and 5-hole designs are not interchangeable."
They weren't particularly expensive in 1996, but of course, that doesn't necessarily mean anything for 2003

.
You could also try using aftermarket hubcaps. Most of them are designed to be quite large, so they tend to fit a wide range of vehicles. We bought some for our Polo 9N after the dealership wanted a whopping 86 euros (!) for a set of hubcaps, and even eBay was asking almost as much for used ones.
I found that the caps at the Gl*bus hardware store were well-made for a very reasonable price of €2.29. They have a metal ring, and the only thing I noticed was that the paint was a bit thin. But hey, for the money we saved, we can buy new ones every winter for years to come...