I agree with what a lot of others have said, if you aren't willing to register both you shouldn't even develop the site.
Personally, if you develop a site, a good site, you should register an entire set:
.com (if available)
.net
.org
.us (preferrably)
Assuming the .com is available, I'd grab that obviously and then the other bulge bracket domains and redirect them. The reason being, someone else will register them if your site is really good.
I also agree with the idea that you should consider a .com variation instead.
Good luck.