You just write the number and 달러. 10 달러 50 달러 That's all. Not like with some other counters where it is object-number-counter (고양이 두 마리).

This stuff is from the shape of the dolla symbol($). As you know the symbol consists of one 'S' and two vertical column. For a long time and even now(and even in the future) we Korean use Chiness character(but the pronunciation is different.) There is a Chiness character '弗' and we pronounce it '불'. That's why we often use '불' as well as '달러'.

불(弗)=dollar 10억 불=10억 달러

달러 and 불 are the same but most people use '달러'(doller)