The pendant style you liked witth the 8 mm round garnet and halo of diamonds is available with a sapphire. The pendant would be made in Germany in 18 K. The cost would be approximately $6,000.
Oval sapphires are available in a variety of sizes and qualities. This is a similar computer generated image set with a sapphire.
I have priced this style with a range of sizes:
The pendant is available in yellow and white gold.
I would like to offer other options. If you like a style I will price it in your choice of gemstones.
Gold chains of an appropriate size would range from $300 to $500.