Meghan Markle could wear a custom-designed tiara worth nearly $700,000 on her wedding day - here's how much the tiaras of other British royal brides are worth

Princess Margaret departed from tradition and wore a tiara that wasn't already part of the royal collection, acquiring it shortly before her wedding to Lord Snowdon in 1960. The Poltimore Tiara, another Garrard creation, boasts cushion-shaped and old-cut diamond clusters and diamond-set scroll motifs surmounted by old-cut diamond terminals, all mounted in silver and gold.

It was auctioned for £5,500 (roughly $7,570) at the time it fell into Princess Margaret's hands, and was recently sold at a 2006 auction for £926,400 (around $1,275,154) — about four times its estimate.

When marrying Prince Charles in 1981, Princess Diana donned a tiara not from the royal treasure troves, but from her family's own aristocratic archives — the Spencer Tiara. This diamond encrusted piece shaped into tulips, stars, and scrolls belonged to her father and was worn by her mother and sisters on their wedding days.

This dazzler is made of a variety of other jewelry — the central portion was part of a wedding present to Lady Cynthia Hamilton (Diana's grandmother) when she married Albert, Viscount Althorp; the topper was given to Cynthia by Albert's great aunt, Lady Sarah Isabella Spencer; and the ends come from a tiara once belonging to Frances Manby, the last known Viscountess of Montagu. The current version was reportedly finalized in the 1930s.

There is no estimate on how much it's worth, but a similar headpiece with 800 cut diamonds and an estimated weight of 48 carats was recently sold by the Spencer family for $225,000.

Even more stunning than the Duchess of Cambridge's custom Alexander McQueen gown was the Queen Mother's Cartier Halo Tiara that glittered against her veil. Featuring three bands of 739 brilliant-cut diamonds as a base, it's topped with leaf-like scrolls and finished with larger round diamonds on top of 149 baguette-cut diamonds.

King George VI commissioned Cartier London to make this platinum tiara in 1936 as a gift to Elizabeth I. It was then re-gifted to the current queen on her 18th birthday, who loaned it to Kate Middleton for her wedding day.

While its value is unknown, a paved solitaire diamond platinum ring from Cartier runs anywhere from $6,350 for a 0.5 carat diamond to $161,000 for a 3.03 carat diamond — so you can only imagine how much a nearly 1,000-diamond Cartier tiara is worth.

Meghan Markle has several stunning tiara options for her fairytale wedding to Prince Harry — the Strathmore Rose Tiara, the Lotus Flower Tiara, the Cartier Bandeau Tiara, or the Cambridge Lover's Knot, which features 19 arches and 38 drop-shaped pearls. It was sold at a Christie's auction in 1981 for more than $747,000 in today's dollars.

However, nothing is traditional about Markle and Harry's relationship. She might stay in tune with their modern wedding and have a custom-made tiara created specifically for her.

Jerry Ehrenwald of the International Gemological Institute estimated for Business Insider a hypothetical custom tiara to cost approximately $687,360. It would be three by 18 centimeters, made of half a pound of platinum, and feature 800 brilliant-cut diamonds (approximately five 1-carat stones with a VVS 1 clarity and D color and 795 .25-carat stones with a VVS 2 clarity and F color) and 150 baguette diamonds (approximately .25-carat stones with a VVS 1 clarity and F color).