My heart goes to you OP, as this is exactly how I felt about myself for many years. It's a horrible set of thoughts to be having about yourself. 
I understand now that beauty is not an objective thing, in any way whatsoever. It's an atmosphere that exists around a person, and that, actually, can be artificially created by putting together different elements: elegant posture, a beautiful scent, laughter, different colours, the tone of the voice, different makeup effects, and so on. These are all small things, but the cumulative effect can be, and is, powerful.
I also no longer believe that the only people who should be allowed to spend time/money caring for their physical selves are the 'naturally beautiful'. My body might not conform to the dimensions of a model, but it works very hard for me and is every bit as entitled to be groomed and pampered!
When a few years ago I wanted to see if I could make myself look better, I read the quote that Bluntness used in her post about ugly/lazy, and found it really intriguing. I decided to embark upon an experiment: to what extent could a fundamentally ugly woman improve her appearance? Could beauty be faked? Approaching it this way, as a test of my ingenuity helped me to short-circuit some similar thoughts to the ones that you are having, 'Surely the only thing worse than being ugly is to be ugly AND vain...', 'People will either laugh at me or feel sorry for me if they see I want to look good...' (I also had someone spiteful in my life who had suggested these things to me, but now I see he was afraid and wanted to keep me where I was). Anyway, the upshot of it all is that now, a few years down the line after a bit of weightloss, some new clothes and grooming routines, I feel really rather attractive most of the time.
Sorry for the long post, OP. I really hope that you buy the jewellery, and that you enjoy looking at it on you. There's loads of support to be had here, on the S&B board, 'princessing' threads etc - we're all struggling with the same kind of stuff. 