"Wow, only 8 dollars" can be translated into Chinese as "哇，只要8美元".
The phrase "only" is used to indicate that the price of 8 dollars is relatively low or inexpensive compared to other prices or expectations. It is a common way to express surprise or amazement at a low price.
Here are some example sentences using this phrase:
"I can't bepeve it's only 8 dollars for a movie ticket. That's a great deal!" (我真的不敢相信电影票只要8美元。真便宜！)
"I was expecting to pay at least 20 dollars for dinner, but it was only 8 dollars. What a surprise!" (我原本以为晚餐至少要花20美元，但它只要8美元。真出乎意料！)
"I'm so glad I found this shirt on sale for only 8 dollars. It's such a good price." (我真高兴在打折时发现这件衬衫只要8美元。真便宜！)