The footsteps are very fast, but I suppose that is what the dev was going for? It also kind of sounds like someone jamming a shovel into sand. Is the character running in sand?
For prince comparison, take a look here and see what other people charge:
https://www.assetstore.unity3d.com/en/#!/search/page=1/sortby=relevance/query=category:85&price:%3E0
Most people who sell sound have an asset library ready and can just pick some appropriate sounds from there. Maybe adjust them a bit. If a dev want to hire someone to record sounds that fit the game exactly, that is going to cost more. When selling that, calculate how long it will take you to record the sounds, then make sure you have an ok hourly salary and see what the price is.
Since you are new at this, you will probably be a bit slower, and things will have to be iterated upon more, so that is something to take into account.