Devices for slow-motion video recording
You may want to look into Sony's camcorder line (even legacy; like the NX5U). 

The NX5U and I think even the FX1000 (which is an HDV Tape Format and can be had used on a place like ebay for under $1000) could do bursts of full 1080p 240+ for a "limited time". 

If I remember correctly the FX1000 by sony could do 240 frames at for 10 seconds. It would buffer the video into internal memory; then queue the tape; then record to tape when the 10 seconds was up. 

It was limited in terms of it's usefulness; but it sounds like based of what you want to use the slow motion capture for; it may be worth looking into to. 

Burst cameras (even the iPhone now does this); will give you a higher frame rate, with limited record time for a much lower price than say going the RED route or Phantom Route. 

Or you could rent a RED, RED Epic's will do 480FPS at 1K; and they can be rented cheap; as they are everywhere... and sit on the shelf most day's of the week by people who own them.