I recently changed my factory fitted steel rims to vw alloy wheels. One thing to note is that if you go with factory branded alloy wheels they will cost a lot more than non factory branded alloy wheels.
When purchasing any alloys you need to ensure that they are from a reputable company and that they have the certification that states how much load can be put onto the tyres. So depending on what you are carrying in the back ask these questions with the dealer.
In my case I emailed a local camper van conversion company who advertised that they sold alloy wheels. Luckily they had a set of four VW second hand alloys that were taken off another conversion. The company was also located next to a tyre fitting company so could all be done in one trip.
I did a deal just over a £100.00 for all four. They might have had a few scratches but this didn’t bother me for where they were going to be used. This was perfect as I was trying avoid paying for brand new alloys and they were vw as well.