Thrift stores or dress outlet stores can be very helpful and inexpensive~ I know for myself I bought a long wedding style dress, or you can check Ebay.
Another option is when you create the sleeves, try using white (fake) flowers at a dollar store. I know I'm speaking of cheap but I'm on a limited budget too. What else are you looking for in terms of this? Are you seeking ways to creating props, like her Star Locket? May I suggest a Tuxedo Mask plush and/or Luna plush?
If you have any other questions, feel free to comment here. =)