Amethyst is a purple variety of quartz and is readily available in large quantities and relatively inexpensive - without knowing the weight of your crystal it is difficult to estimate what its value may be. For reference and comparison, this link may be helpful: https://www.mineralminers.com/html/amethyst_crystals.stm
It is unclear to me what the phrase "cost of partial ring creation" means ... are you considering having a ring made with this amethyst crystal piece? or finding a jeweler willing to cut the crystal into a faceted amethyst?
It's a chunk of Amethyst people use as crystals or mineral specimens, you can find them in shops ranging depending upon the size of it from $5.00 to $100...
Your sample isn't particularly clean nor is it a top colour.
Yeah it's a pretty crystal but probably not suitable for cutting as a ring stone unless you specifically wanted that one for sentimental reasons etc. It's not clean rough, would probably only work as a cabochon.