If you can’t spend much, your best bet is this Marni Ring. It's a popular piece, while not very pricey. Another strong contender for your wardrobe is this Marni Ring. While the price of this item is competitive, it will certainly attract a lot of attention.
If you're looking for something in between pricewise, why not check out these Marni Earrings. While the price is very reasonable, this item is an easy wardrobe update. It's also worth looking at this Marni Bucket Bag. This item is extremely popular and, just as importantly, not too pricey.