Offering pay is a good start, but the lack of replies is probably due to the vagueness of the offer.

"Ice cream store game" is not actually very descriptive. You may know what that means in great detail, but the potential artists don't know what that entails.

The style "anything" is not terribly helpful. Its nice to be able to pick any style I want, but it's better to be specific since contrasting styles rarely look good.

Giving the example image for style is helpful... well, it would be helpful, but the image is nearly useless due to the huge "SAMPLE" pasted over it. A more subtle barely-visible watermark would be better. Better still, no watermark at all. I'm sure there is a fear of the artwork being stolen, but it is rather unlikely. However, I can understand the concern. You need to assess whether the risk of your art being stolen outweighs the ability to land an artist willing to help out.

"I need you to completely replace ripped art and IP with original work." is a scary statement to many artists. Unless the total work involved in this request is no more than a quarter the size of that sample image, $50 is probably not going to be enough to cover the huge effort involved. If you can provide gameplay footage and graphics of actual working game, you should do so in this request. Artists want to know how much art they will be replacing. Show all the art that needs to be replaced. If it's all ripped art and IP not owned by you, you don't need to be worried about people stealing it; it's already stolen. And you're doing the right thing by getting it replaced with legit art.

A lot of artists want to be sure their work will see a release day, but there is not much to convince them that will happen. You are unsure how many years it will take for a playable demo. That's somewhat normal, but it isn't helping to attract artists. If the art were to be released under a permissive license, that might be encouraging since the artist has the hope their work on this project will be put to good use by someone even if this project doesn't take off. You know your project will take off, but the artist doesn't know that.

I'm sure you've seen this already, but just in case: Here are some pretty helpful guidelines for writing an effective art request: http://opengameart.org/forumtopic/how-and-when-to-write-a-good-art-request

Then again, you might just need to wait a little longer for the right artist to come along and see this request. Either way, best of luck! :)

I am interested in this project and sent you an email the other day. I made some strawberry ice cream today. Let me know what you think. 

You can check out some of my other work at http://christiandasilva.us/2Dart.html and can email me at christiandasi@gmail.com