店员：Are you ready to order? 我：Yes, I'd like to have the #2 combo. 店员：You want the supreme or the regular? 我：Is there a price difference? 店员：What's that? 我：I mean the price of "$8.99" on the menu, that's for the supreme, right? 店员：Yes. 我：So the regular would be a bit lower? 店员：Yes, $7.60 for the regular. 我：Does the "supreme" one worth the price difference? 店员：What's that? 我：Never mind, I'll just have the supreme（我也意识到问题确实问得有些多余, 因为店员不可能给出"Yes"以外的回答）.
店员：Are you ready to order? 我：Yes, I'd like to have the #2 combo. 店员：You want the supreme or the regular? 我：what is the difference, please? 店员：the superme is .... and reguluar is .... 我：great！ I'd like to have one regular please! 店员：Yes. that is $7.60 我：Here you are, thank you!
I don’t see anything wrong with your first question.
In your second question, "worth" is not a verb. But, if your pronunciation is not an issue as you said, the store employee should've understood what you were asking.
一个中国人（我本人）走进一家美式快餐店。
下面是店员与我（英语发音还行, 但说话有时并非英语思维而是中文思维然后设法翻成英文）的对话：
店员：Are you ready to order?
我：Yes, I'd like to have the #2 combo.
店员：You want the supreme or the regular?
我：Is there a price difference?
店员：What's that?
我：I mean the price of "$8.99" on the menu, that's for the supreme, right?
店员：Yes.
我：So the regular would be a bit lower?
店员：Yes, $7.60 for the regular.
我：Does the "supreme" one worth the price difference?
店员：What's that?
我：Never mind, I'll just have the supreme（我也意识到问题确实问得有些多余, 因为店员不可能给出"Yes"以外的回答）.
大家帮诊断一下，我的问题出在哪里？由于店员是美国人，说标准的美式英语，所以我感觉一定是我的问法有些问题。但也不知道问题出在哪里？是不是“price difference”这个用词让人感觉陌生或突兀 以至于店员一时间没弄明白我想问什么？如果要表达同样的意思, 用标准的美式英语该如何提问？
当然也不排除有可能是我当时发音有问题（没说的很清楚）或者当时环境略有嘈杂等的可能性。
后来写成文本感觉加个“one”也许好一些，看来加错了 ?
按照我们中国人，根据环境和谈话内容，都知道你要表达的意思。其实，那个店员也应该听得懂。我初出来的时候，办事是往往说不出一句整话，只所一个关键词就能沟通。对方想和你沟通，就都听得懂。菜单标号就是为了店员与顾客沟通方便，就是为了避免误会。只要说一个No.2，对方就应该完全明白，其它都是多余的话。
首先price difference是中翻英，我觉得英语应该是 different prices，或 difference in prices。你可以换一个问法：Are they at same price? 或 Are the prices different？
Does the "supreme" one worth the price difference?
这句简直太中文翻译英文了，我会说 Is supreme a better/good deal?
不一定正确，仅供参考：）
but it seems better to say: is supreme worth that price?
my two cents.
(发自我的文学城离线浏览器)
https://bbs.wenxuecity.com/mysj/275453.html
https://bbs.wenxuecity.com/mysj/275453.html
https://bbs.wenxuecity.com/mysj/275453.html
https://bbs.wenxuecity.com/mysj/275453.html
店员两次问“What's that?”都是上升语调的那种。
这通常是表示没听太清楚的意思。 如果是下降语调的话那可能就是不满或质疑的意思了。
Regular?
Worth it or not is up to you to decide
店员：Are you ready to order?
我：Yes, I'd like to have the #2 combo.
店员：You want the supreme or the regular?
我：what is the difference, please?
店员：the superme is .... and reguluar is ....
我：great！ I'd like to have one regular please!
店员：Yes. that is $7.60
我：Here you are, thank you!
https://bbs.wenxuecity.com/mysj/275453.html
https://bbs.wenxuecity.com/mysj/275453.html
1. Is there a difference in price (note price, not prices as someone earlier wrote).
2. Is the supreme better.
In your second question, "worth" is not a verb. But, if your pronunciation is not an issue as you said, the store employee should've understood what you were asking.
https://bbs.wenxuecity.com/mysj/275453.html
https://bbs.wenxuecity.com/mysj/275453.html
https://bbs.wenxuecity.com/mysj/275453.html
有木有看过中国老式有声民国电影？不接地气的念书本一字一句的台词，今天谁受得了啊。
多看英语电视电影，不要字幕，跟着学，坚持几个月，就会话自由了。
这也是很多美国孩子，会说英语，不会写，和中国留学生整个一颠倒过来。
书写英语和对话英语，差了太多。
你要跟人对话却一字一句滴念书，等你念完，人家早就不耐烦，跑没影儿廖。