In the situation that you need to merge the currency with text to make a sentence in one cell, you are better not to directly put the currency and text together with the CONCAT Function or Ampersand. The dollar sign will disappear in that way.
To properly display the dollar sign, you will use the TEXT Function to format it to keep the dollar sign after merging.
For example, when merging "Apple" and "$500" together, the "$500" becomes 500 without the dollar sign.
Where TEXT(B2,"$0.00") is to format the number to be the currency format and to keep two decimals.