The gun and the operating system are designed for 40 S&W, and have an excellent service life with that cartridge. The action should run nearly forever with 45acp, as the operating pressures involved are significantly lower.
The ergonomics of the full sized version are great. In my experience the "mini" framed versions are good as well, though obviously shorter.
Maintenance of the 8000 series rotating barrel system is quite easy. I have seen several make the claim hat rotating barrels are picky about lubrication and need to be run wet. This is NOT my experience with my 8040, which happily shoots any brand of ammo I have used thus far, and with only normal levels of lubrication on moving parts. In my experience the 8000 series needs no more attention than any other pistol.
The Beretta 8000 series is a great group of pistols. About the only problems some people have with the mini version is that it is strictly a 2 finger pistol unless you use a mag with a finger extension, then no problems.
I believe you can find the 8045 F Mini-Cougar selling for around $500 to $600 on Gunbroker. Possibly more for one still new in box.