Thanks. Your room size is 3000ft^3, which is classified as 'medium' by
Bassaholic ranking.
Which means if you buy a subwoofer that's rated for a 'small' sized room, and you try to hit reference levels (around -10db from reference level on your AVR, which is the loudest most people play in their home theater), then the subwoofer will run out of SPL before you can reach that level.
To help find 'medium' rated subs, I've created a 'subwoofer comparison' thread
here.
You need to spend at least US$500/ea to hit this rating, which is okay, since your budget allows for it.
My thoughts:
1. At the minimum, you need 2 subwoofers to get good seat-to-seat consistency and to get rid of frequency nulls caused by room modes (or standing waves).
2. Also, since your goal is primarily movies, my recommendations will be only for ported (not sealed) subs, since they reach an octave lower than sealed subs, and will be immediately noticeable for movies.
3. For you room size, if I give a recommendation for a 'medium' size-rated subwoofer that means that subwoofer can hit reference level of playback, but with some degree of distortion. However, if you get more capable subwoofers (say one for 'large' room) and you hit reference level of playback, then the 'large'-rated subwoofer will have more headroom available, and will play with less distortion than a 'medium' sized subwoofer hitting the same levels would. Plus, a 'large'-rated subwoofer will hit lower octaves, so will be more beneficial for movies.
So I'm going to give you 2 recommendations, depending on what you want:
1. If you just want enough output for your room size, but without much headroom, then I recommend Two of SVS PB-1000 (rated for a 'medium' room) for $1000/pair.
2. If you want more headroom (aka SPL) in your subs, but you're willing to accept the larger size of the sub, and you want a subwoofer that can hit a lower octave in frequency, then I recommend Two of "Monolith by Monoprice 12in THX Ultra Certified 500-Watt Subwoofer Amplifier" (rated for a 'large' room) for $1400/pair.