The main progression in Peak Rider is all of the unlockable gear and characters in the shop. Some of them are locked until you rise to higher ranks, but getting there is easy and there's more than enough to buy for now. Collecting the lines of gold coins which usually trail before ramps on stages is obvious a decent way to rack up cash as you go, but it's not necessarily the most efficient. There should be a fair amount of challenges available to you, however. You'll be tasked with beating the scores of other players, or scoring a certain amount of points. Each of these challenges will reward you with gold that you can use in the shop, and by doing challenges you'll soon be racking up plenty of cash.