I don't know about board games, but I've had out-of-print books, CDs and video games that I've tried to locate. If it's something I really want, I do usually get it eventually, and most of the time at a reasonable price.
For me, the key is patience. When I was looking for the Jesus: Son and Savior
book from John Paul II's Wednesday audiences (which right now is at $68+ for a used copy but at the time was something even more insane like $300+), I just bided my time. Eventually, someone came along and was offering a used copy in great condition for $14. That I can do.
There's a website camelcamelcamel.com which allows you to track Amazon price fluctuations. They'll even email you once the price drops below a certain threshhold that you set. That's the route I would recommend.
My brother has had success with eBay. He simply keeps an eye out for the item he wants and knows ahead of time what he is willing to pay. It often takes awhile, though. Eventually, after getting outbid many times, everything lines up and he gets what he wants for the price he wants.
I think that with out-of-print items, you have three types of sellers. First, there are the scalpers who know nothing of the product besides the fact that it is out-of-print and they charge an exorbitant amount figuring that eventually someone will come along and buy it at that price because they have no other choice.
Second, you have the collectors who know the product inside and out and they realize how rare and sought after the item is. They, too, set their prices high expecting that someone will eventually come along and buy it for that price because they know the value some people ascribe to it.
Third, you have the regular person who might not even realize the item is out-of-print, they just know they're tired of having it sit on their shelf and they want to get rid of it and make some money in the process. Thus they often price the item to sell as they would at a garage sale rather than at an antiques road show. These are the types of sellers I wait to buy from.
They don't come around as often, but they do come around eventually.