Where I work, we judge star stones using several guidelines. Here are some that may help you judge the value of your stone:
Color - What color is your star sapphire? Blues are most valuable. There are also fancy colored ones like pink, green, grey, black etc. Those are less valued than blues. Whatever it is - is the color saturated? Is the tone balanced? Is the physical distribution of color even or is there color zoning?
Clarity - Is the material relatively clean or are there visible inclusions? Where are they located? Are they obvious or subtle? Do they affect durability? Is the material semi-transparent, translucent, semi-translucent or opaque?
Cut - Is the cabachon balanced? Or is it lop-sided? Is it top-heavy or just right? Is it well-polished?
Star - Is the star sharp? Are all the legs present and complete? Is it centered?
Size/Carat - Large sized stones of good quality over 5cts are rare and therefore more valuable!
My experience...I sold a top quality 10.74 carat Blue Star Sapphire last year. It was perfectly round, although a little heavy on the bottom. Pure blue color with no greys. Good saturation with a medium tone. Translucent. Clarity was good. Superb finish. US$14K. And that was already considered a reasonable price.
Pricing a stone is very. very complicated. However, as a very very rough estimate - an average stone of under 5 cts may sell for $60-300/ct per carat (varying widely from stone to stone and location to location).
If you send me a clear photo of your stone, I can help make a gauge as to whether your stone is valuable or not. If you don't have photos, use the guidelines I've given you and check a copy of the Guide - which gives you american wholesale prices of all stones.
Me: I'm a gemologist & part-time gem dealer