What's the difference between “问一下”，“查询”， “询问”？
Would it be appropriate to say any of the following?
我想查询您…

This usage is wrong. 查询 should be followed by the object being asked for, not the person who is being asked. The correct usages are

我想查询[sth]。
我想向[sb]查询[sth]。

Example:

我想（向您）查询从北京到上海的机票价格。


我想询问您…

This one is correct. 询问 can be used in three ways:

我想询问[sth]
我想询问[sb][sth]
我想向[sb]询问[sth]

Example:

我想询问从北京到上海的机票价格。
我想询问您从北京到上海的机票价格。
我想向您询问从北京到上海的机票价格。

Both of them are formal but never too formal to use in daily conversations; I use them from time to time when talking to a service personnel, especially when over the phone.