As Vee_Que said, paint the wheels silver - alternatively there might be a way to fit the metal hub caps from an earlier 240. I might be making this up but I think
@lasercowboy did this?
However as above, 15" alloys are definitely affordable. I have a set of 5 Virgos that I'm looking to sell soon if you're interested.
Here's a picture of them on my car
http://i.imgur.com/tzzgK4h.jpg