If you're okay with being in it for the long haul, then you might be okay. Pins spike, then drop, then sometimes spike again...Jessica DA LE 100s, which were some of the biggest Grails in their days, would go for $300, then drop to a little over $100. Stuff goes up and down all the time. So while you scope up the cheaper ones, maybe the craze will die down and the prices on the more desirable pins might drop some.
That said, your hard limit of $15 will definitely change over time. I used to flinch at $30, then $50, then $75, then $100- now, I have so few Wants that I'm only really buying Grails once every year and a half, so I can afford to do what I have to to get them. So sometimes it's between getting multiple cheaper pins, or getting one really in-demand pin you want.
That said, make sure you search Pinpics for other move/film related pins...there are quite a few out there besides the marquee collection.
Good luck on whatever you decide to do, and remember, don't beat yourself up if you miss out on a pin- they'll come around again, and sometimes, for a better price!