Up to date inventory info from retail store on the website?

Ok i m not sure if this is the correct place to post this, so i m sorry if it isn't.

Ok i have no programming knowledge at all, and I m going to hire someone to do the below task. But, I wanted to have at least a decent understanding of what it takes to set something like this up, the time it would take, and the cost. So here goes:

How do I set up my site say like walmart.com , where basically customers have the option of checking whether a product is being sold and in-stock in the local Walmart store and the latest price of the product?

Would i have to get a software developed that would fetch the above data from my Point of sale system in my store and would update the website, or are they any such softwares available?

I m really not at all knowledgeable in this field, so if you can guys can help me out in any way, i would be really grateful!! Thanks!!