Hi ladies!!
I'm pro silk flowers on a wedding but it depends on the arrangement, for example: aisle decor on chairs YES (flowers and greenery), bridal bouquet: NOP, groom, groomsmen and bridesmaid bouquets YES
There are some great and cheap options in Ali Express but they are from China, you need to take your time and look into all the options and it takes about 3 months to arrive.
Another option is to look for floral design vendors in the area outside from the resort, usually when you buy the flowers in the hotel, they are very expensive (2x, 3x than local) and if you hire an external vendor, the hotel charges a fee but most of the time it's even cheaper to buy centerpieces, bouquets, boutonnieres, arch/huppa arrangements etc. outside than buy them in the resort!
I wouldn't recommend to do your own natural flowers arangements because Now Sapphire is in the middle of nowhere n Riviera Maya and you will need to go all the way to Cancun, plus they don't speak very good english in the local flower shops.
Another tip: peonies in Mexico are one of the most expensive flower but there are other type of flowers call "garden roses" that are very similar and look amazing
Happy planning!!