I assume you welcome responses from women, too? I had one for my first marriage, and it cost $1,500. MONEY WELL SPENT.
In it, we agreed that we would walk away with what we each brought into the marriage, any inheritances would stay with the person, and we would evenly split what was accumulated during the marriage. Also, neither party would be entitled to support from the other. Since he had the history of being a higher earner, I knew agreeing to forego support was probably to my disadvantage, strategically, but reasoned, if the situation was reversed, I wouldn't want to support him either, so it was in keeping with my values.
Within months of the wedding, he was a totally different person with all the signs of an addiction problem, and was removed from his own company by his partners. His income was $0 during the 17 months we were married. As I was paying all our bills and giving him an allowance to boot, his addiction consumed ALL of his assets. Toward the end of our time together, he managed to get into my chequing account, and, over 3 weeks, drained it of the majority of the funds.
Despite this, he would've been entitled to another $6,100 from me in spousal support (total, not monthly, due to the brevity of our marriage). I'm sure he would've pursued it, but the $1,500 prenup prevented it.