Hard to get steel rims for 16" +, way too heavy in that size IMO.
$600 for the rims alone isn't that great, that depends on the type of rims tho, if they are relatively light, that would be great. You can get brand new rims (16") at about $180 a piece (relatively heavy, not sure it fits E36/E46s). Anything fits German cars are not too cheap when compare to JPN/NA cars.
If those rims are $500 include shipping, that would a good deal.