Auto Add to Cart for shopify site

I need something that can automatically add a product to cart and complete checkout steps on shopify based website. This is not for shoes. I will provide website on request as I do not want it to be searchable. May need to auto refresh until finds item Select items once available on website Select Size & quantity of 2 Add to cart Auto Checkout Completes Whole Process In Matter Of Seconds Details: I am a newbie, so not sure if this could be done. I don't even know how to specifically ask for this.. Optional: if a size is sold out  or unavailable then include option to pick the next biggest size Please be fair & reasonable in pricing. I am not a reseller, I'm just tired of missing out on these over and over again at retail prices. I don't want to insult anyone by being cheap, but these items are for personal use and cost no more than $50, so I don't want to pay more than that for a bot. Thanks