I shopped for a long time for aftermarket pieces like this and found the universal advice to be that these parts cost less when they're delivered, but after you pay someone to make them fit well, you will have spent as much as if you'd gone OEM. I got this advice from custom body shops, both high end and low, and from other forum members. One wrote bluntly, but correctly, that "if you can't afford to go OEM, don't go." I've also seen claims of fitment percentage, such as "90% perfect fitment" as if one can say that an imperfect fit can be assessed by its fraction of a perfect fit. I'd hate to be looking at an aftermarket part's installation and notice that the 10% I didn't get is front and center and forever an eyesore.
For shopping for parts, I can offer this advice: Find the best price for the OEM part on the internet and let your local parts department manager have the opportunity to beat it. I learned this because I am a week away from completing an OEM front bumper cover replacement project and I bought all of my OEM parts from www.getbmwparts.com
for a lot less than I would have paid retail. Because my local BMW dealer body shop quoted me the best offer to do the actual paint and install I also gave the local dealership parts guy the packing list for my parts for him to sign in order to acknowledge the parts' receipt at his body shop. He saw the prices, and saw where I got them, and told me that if I had shown him the list of parts and the prices of the items in the web site's shopping cart, he would have matched every item's price.
So, shop around for the parts yourself if you want to on eBay and at OEM parts web sites, and your local dealer may be able to match the prices that you can get online for OEM parts.
Sorry to write so much, but other forum members took the time to warn me about aftermarket parts, intentionally or not, so I feel I should pass on their advice.