Welcome to CS.
What do you want from the machine? Do you just want to be able to offer the occassional coffee to people browsing the store?
Or do you intend to sell coffee?
Have you considered a grinder?
What coffee beans would you use?
A $500 budget does not really seem feasible to me. Most people here will advise you to spend at least that on the grinder.
I think you would do well to chat to a sponsor in your area if possible.
Or keep posting here. Theres lots of us obsessed people around to answer!