Devices for slow-motion video recording I'm interested in shooting slow-motion videos of sports (eg. ping-pong, badminton; for analysis and such). After trying an iPhone camera I wish to get something higher quality/more crisp (ideally 1080p@240fps).
However, finding something decent at an affordable price-tag seems to be rather difficult. hispeedcams.com is a quite good source for this purpose. Here are some notable finds.
research
rather professional solutions (too expensive)

RED RAVEN &quot;[...] 4.5K Full Format (FF) at up to 120 fps, or in 2K FF at 240 fps, [...]&quot; (at $8,950.00 (USD), €9,030.00 (EUR), £7,970.00 (GBP))
Panasonic AG-DVX200 &quot;120-fps Variable Frame Rate&quot; ($3,795.00)
SONY NEX FS700 &quot;120fps at 4K&quot; ($3,499.00)

dedicated high speed cameras (more than needed)

edgertronic SC1 &quot;- 701 fps @ 720p: Color 8GB DDR3 Install IR Filter - 400-675nm response&quot; ($5,495.00)
chronos 1.4 &quot;1,057fps [at] 1280x1024&quot; (2,999.00$

action-cams (too limited): (&quot;240fps at 720p and 120fps at [...] 1080p&quot;)

Sony FDR-X3000 ($348.00)
GoPro Hero 5 Black ($399.00)
Yi 4k+ ($339.98)

DSLM/MILC (which would also be nice as default photo cameras but don't have a optical TTL view finder)

Panasonic GH5 apparently 1080p@180fps (€ 1.999,00)
Sony A6500 1080p@120fps ($1,399.99)

It would be nice to have something more versatile than action-cams, but less expensive than those professional devices. As I don't want to shoot slow-motion only, cameras specially designed for that aren't really what I am looking for either.
This leads to the (still quite expensive) GH5 (or similar DSLM) and also to a few
questions:

What should I look for in gear for a beginner?
Is there something (DSLRs/DSLMs) in between (regarding price) GH5 and action-cams (similar to a6500) supporting slowmo ?

Some specifications mention that high-speed capture is only available for a few seconds

Is there always a maximum on how long can I capture slowmo if it is not noted?
If a camera is advertised with (eg.) 8sec 1000fps, at which rate could it record permanently then ?


note:
I have asked for DSLRs on photography already with comments mentioning the GH5 only - I can remove this partial question if it is not fitting
I have split off the SDI part-question here.
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.