The final cost of demand side platforms varies depending on the features and services it provides. Typically, DSPs charge a percentage of your media spend or a flat service fee. Costs can also depend on the complexity of your campaigns, their frequency, and other critical factors.
You'll see prices from $1/click, $10/day, 17% of ad spend, $12,500/month, minimum $50,000 ad spend. So as you can see, unlike other software services, the pricing rubrics aren't standardized in any way that allows you to meaningfully develop a range from high cost to low cost. Instead, it will mostly depend on how many ads you need and how many clicks or conversions you receive.