That 12 mm trill in pink spinel will weigh approximately 7-7.5 c,
properly cut. In the finer pinks, expect to pay $4500- 6000 for the
stone, wholesale. Then you have to find it. If the color is really
nice, and the cutting is really superior, well, lots more. The rough
spinel required to cut a stone such as this is generally not
available unless one is in the right place at the right time, with
lots of cash. I certainly have none available, but could suggest a
possible source if you wish to contact me privately.
If that doesn't sink your customer, you might suggest pink
tourmaline, perhaps. Pink sapphire in that size will be even harder
to find, and quite a bit more $$$.