Hi altaran,
There is a Rating script over at Solspace which I have heard is very good. I have purchased software from them before and they always work pretty much out of the box so to say.
You could also feasibly create this kind of functionality yourself with weblogs and then saving numbers in custom fields and incrementing them and then display them on the front end. A bit more work involved obviously but definitely doable in that way.
A few others for you to chew on also are :
EZ Rate
EE Rating Module by Silenz
Unobtrusive AJAX Star Rating Bar
Regarding the license situation you are probably going to need the full version of EE to get what you want working if you don’t go with a module and so you would need to pay a higher value than normal. Whether or not you would have to pay the largest fee would be up to sales and it would be best to shoot over an e-mail to them, let them know what you are doing and see what they say. I would have thought they would be all right with you purchasing the lower value version and then just paying the difference when the site is ready to go live but don’t quote me on that. As I said before it would be best to e-mail them to find out about that one.
Should be something their for you to chew on! 😊
Hope that helps?
Best wishes,
Mark