I did one client's for just a little live price and balance display for bittrex I think it was just a little 100px * 100px he wanted to stick the little app in the top right of his desktop. It did it for like 0.01

 Id need some more details to give you a pretty spot on quote... A really complicated full dashboard I made for someone to use on a separate monitor for live feeds of graphs and prices few grids special calculator and few buttons.. after all his changes and modifications over a month period I think i only ended up charging him 0.10 for the whole thing (this was a entire app full of streaming data and a couple buttons for tasks) It just depends what you want.. and what I will need to make on the fly if I haven't already made it before.