I am a member of quite a few boards and most use a New Topic post to announce the giveaway, with a limited time to enter and requesting those interested to post a reply to the thread such as "I'm in" or another specific "phrase" to weed out the skimmers who are looking for the free loot but can't be bothered to actually *read* the posted instructions carefully. The post # becomes the individuals lottery number for the random draw.
I do have a problem with more than a basic minimum post count as many of us who are newer members do follow the proper etiquette of forums and thus do far more searching and reading instead of posting for however long it takes to feel that one has something to share... well, at least that is what I do.
As for shipping costs.... yes, this IS an issue..... While it may seem unfair to some, the prize will most likely be at your location and shipping the prize across town is going to cost significantly less than shipping to North America, the Far East, EU etc. Perhaps a base shipping cost could be set with the winner to pay whatever additional costs above and beyond that base rate, should it be required, would be the fairest way?!?!? Frankly, the other boards I've been on have always had rather small items as giveaway prizes and shipping wasn't an issue. On the 3 boards where the prizes are rather large and heavy, it seemed to always be a company offering the prize and they were will to ship it anywhere required.... Your situation is different as the manufacturer has already shipped it to YOU.
Dave, the good news is that YOU are the boss, it's your show (pun intended) and if someone doesn't like what you do, they can go get their own show.
In the end, I'm fine with whatever you do.....
Regards
Christian