Ok, I think you can just buy them if you like. They are very cheap. For example, you can buy them at $10. Of course, there are some types which can cost $40. But it is still not expensive. And also, they have many cute frames, maybe you will like it. In my opinion, you can just buy them on online shop, such as eyecandy lens which are popular with many people because of their wonderful products. So you can have a try.
I see some circle contact lenses at https://circlelens.net/. Most of them are priced at $32. There are also contact lenses less than $30. Besides, i also some wonderful circle contact lenses at https://lenscircle.com/. But i didn't observe their prices. So, i am not sure how much they charge. You can go their sites and check it yourself. Hope this help.
As a matter of fact, a pair of circle contact lenses would not be very expensive, as they are made at a low price. However, sometimes nice contact lenses of prime quality also can cost you a lot. Generally speaking, a pair of them will be about 50 to 100 dollars. If you really want to find some cheap stuff, you can browse through the Internet to see which place is good. Amazon and MaxMart are good options.
They are not expensive. You could find some circle contact lenses at https://circlelens.net/. Their average price is about $30. If you want some wonderful circle contact lenses, you could still search online. You may go to ebay or walmart online store to have a look. After comparing them at both price and color, you could choose the suitable one.