linking a textbox to a cell

I have a text box linking to cell A4 that contains '$20,000', but the text box is displaying '20000'. I'd like it display the exact same thing that is in the cell. I figured out how to add the $ by making another cell ='$'&A4', but I cannot figure out to make sure the comma is included. The 20,000 value can change and I'd like the text box to change too. Thanks in advance!