Ok. go into settings, and then tap on "keyboard". In this screen, you'll get a list of keyboard layouts (usually just the one). It'll have the language and region
For me, this is "English (United Kingdom)"
Since we don't use the dollar as currency, the dollar symbol isn't on the first page of codes (but ? is). To get to $, I need to tap the "&123" key and then shift right (right pointing arrow) and there I find the $ key.
Or you can press and hold the currency key you do see and choose from a list of other currency symbols.