Tips to buy your first Shawl (Manton)
Size of Manton
They should be square-shaped, at least 140cm x 140cm (55″x55″), not including fringe. There are some that are somewhat smaller, but they’re just too small to dance with. Of course, there are much larger ones, especially vintage ones. But again, it depends on your height and strength. They may be called piano shawls to distinguish them from the smaller shawls used for fashion.
If the shawl is resting on your shoulders and the fridges touch the floor, the shawl is too long for you.
Photo samples: If you are holding the shawl in a triangle with stretched out arms, your hands should fit within the material and it should cover your bum, like on the picture above.
The black shawl on the picture the dance is trying on, is too small (her hands are at the very edge of the material and it barely covers her bum), notice how the fringes are not very thick and they look flimsy.
The blue one on the right is a little larger, but still on the small end; the fridge quality is slightly better, but notice the wrinkles and tangling, which is more likely to happen on cheap fringes. The more weight, the better they move and the more they last. The two performance pictures have the right shawl size and good quality fringes. 
Fringe (Flecos)
Tighter, thicker and/or longer fringes = pricier & heavier, but will move and look better.
the more intricate the macrame (knots)= pricier, but it will catch more air.
Embroidery
Generally, the tighter the embroidery, the heavier and the pricier the shawl gets. You can also get plain ones, often called “rehearsal shawls”, but I would not recommend these: they slip easily down the shoulders and often the balance between the wright of the fridge and the material is of and they are hard to work with and feel completely different than the embroiled ones. So some embroidery is recommended.
Price
It varies so much depending primarily on the material (silk ideally), the macrame and fringe quality, the size and the embroidery. the gorgeous shawls at the top of the page, are easily $800-$1200 each or more. The performance ones, likely aver $500 at least, and the other two samples (the girl with the black one on the shop and the dark blue one, could be $120-$180, I am guessing.
While learning and in performance
Avoid buttons, jewelry, flowers in the head and if possible wear shoes with laces instead of buckles to avoid getting the fringes stuck on them, specially when you are starting.
Care
Never wash your shaw or soak the fringes. You can steam it or hang it in the washroom and let shower run for a bit with hot water, the humidity will help the fringes straighten up.
Resources
If you are on a tight budget, of course you could first try eBay or similar and see what you can find. But look at the pictures carefully and ask for the size. Otherwise, check out these sites. A decent shawl starts around $250, but there are polyester rehearsal shawls in specialized flamenco dance stores that have the right size and are around $100. there are so many types of shawls and most are for wearing, so be specific and google: “manton para baile” or flamenco dance shawl
eBay (a great way to get your first shawl) http://www.ebay.com/bhp/spanish-shawl
flamencoclosetcreations.com (economic shawls, around $150)
esflamenco.com (a range in quality starting at around $200 – over $1000 )
flamencoexport.com (similar to “esflamenco”)