A designer costs more than the app made last month. This costs $49 and is finished.
$49 flat · instant download · commercial licence included
A commissioned app icon runs $300 to $1,000 and takes a brief, a queue and a revision round. That is a rational price for the designer's time and an irrational one for a solo product that has not earned anything yet — which is why so many indie apps ship with the icon that was meant to be temporary.
$49 is the number that fits between "make do" and "commission it". You are buying the finished result rather than the process: the selection is already done, the file is already prepared, and there is nothing left to schedule.
The standard licence is worldwide, perpetual and commercial. Use the icon on any platform, in any number of your own products, in your store listings and your ads, modified if you prefer. No attribution line, no renewal, nothing to track.
The one thing it does not give you is exclusivity — the icon stays on sale, so someone else may licence it too. If the app grows into something you want to defend, the exclusive buyout takes the icon off the market for good.
1024×1024 for the App Store, 512×512 for the Google Play listing, five smaller sizes for the web and the desktop, all flattened and opaque on a full square canvas. Upload them as they are — no exporting, no flattening, no hunting for the size that got rejected.
You could make one yourself. The annoying part — trying, discarding, and preparing the survivor for the stores — is already done.