The 33 megapixel Leaf backs can be worth looking into if you don't need long exposures and don't want to spend too much money. Concerning second hand if you can get an Aptus 75 with a lot of use (they don't really wear out, but price still get lower) the value for money is really hard to beat.
I own one myself (I'm the third owner of it) and I think it is great for a tech cam because
- despite its age the screen is good enough for accurate focus check
- histogram and highlight / shadow blinkies and point-to-check is very good
- 33 megapixels is high enough to give similar quality as 4x5" film, and low enough to avoid the need of the most expensive Rodenstock retrofocus lenses, it is a great combo with Schneider Digitars optimized for f/11.
- low color cast issues, does not require retrofocus lenses
- no wakeup procedure, just plug in the flash sync cable and off you go
- the sensor size 48x36mm I think is the best sensor size tradeoff for tech cams, 44x33 is a bit too small and 54x41mm does make movements a bit limited on many lenses.
- good color accuracy
The disadvantages of this old back is that it is a bit slow showing and zooming in pictures and that it has a fan which is a bit noisy (always runs full speed when on a tech cam). The screen is indeed not good in direct sunlight either but never really found that to be a problem, in the rare cases I shoot in midday sun and the sun happens to shine on the screen I bring out my focusing cloth that I use for the ground glass.