If the poster gets a prize, who gets it, the person presenting it or the first author?

A prize is typically given for both content and presentation of a work, so a typical fair way to handle prize money, whether for poster or paper, is to offer to split it evenly amongst all of the co-authors. Co-authors who feel they have not offered a full share of work might choose to decline their share, but the basic assumption should be an even split. To do otherwise just opens the opportunity for much interpersonal conflict over a generally quite small amount of money.

Remember also that the most significant value of a poster or paper prize is not typically any money that happens to be associated with the prize, but rather the increase in your personal credibility and future prospects that comes from the recognition.

If the prize is for the poster, then logically and morally all coauthors of the poster -- anyone who is entitled to list the poster on their CV -- are recipients of the prize and entitled to a share of the prize money. It doesn't matter if you are first author, second author or twenty-seventh author, and it doesn't matter if you presented the poster or not. As I was arguing in this answer to a closely related question, "Best poster award" has a pretty clear meaning in English (or the language of the conference), and I don't see a case for questioning the intent of the conference organizers in using this language, so there really isn't much room for debate on this point as far as I can tell. If they had titled the award "Best presentation award" or "Best poster and presentation award" then we would be having a different discussion, and then the argument "A prize is typically given for both content and presentation of a work" in jakebeal's answer would be relevant. But they didn't, so it isn't.

Now, logic aside, this is also a question of human relations, so whether it is worth making a fuss about some small amount of money that comes with the prize depends on many additional factors having to do with the personalities of the people involved and the power dynamics of the situation. I don't feel I can advise you about this. But from the moral point of view I think the situation is completely unambiguous.

Hope this helps, and congratulations for the prize!

A poster alone does not get the price it is usually judged together with the poster presentation, thus the presenter has a big influence too. I would assume the presenter will get the price, but depending on your collegaue he might share the monetary value with you (if any). On my poster award the title of the poster and authors were listed too. So if you are intrested to put on you CV you might still be able to do that as long as the authors are listed on the certificate.