Hey there!
After reading your project's description, I can assure you that such an application is very doable. It's pretty simple and basic. I guess the purposes is simply listing products for sale on a Facebook page, with a picture, a description and a "Buy now" link that redirects you to PayPal.
If I'm given all the details and the layouts (even a sketch), I can finish the app in less than one week. As for the price, it's negotiable if it doesn't fit your budget, so you don't have to worry about that..
Feel free to PM me anytime you want, I'm always available