When I first read your title the Smith & Wesson 340 Scandium J-Frame revolver came to mind. A .357 5 shot 12oz pistol, perfect for backpacking. The only problem is they are close to $1000 and hurt like HECK to shoot. I had a full weight model and it was not pleasant.

Your problem is when a gun gets lighter the felt recoil increases. (I'm sure a physics professor knows this)

You mention a .45 which is a proven caliber, and I don't think recoil is bad with these. It is a slow Thuwamp opposed to the sharp Crack of a 9mm or.40.

You can get a subcompacted Glock G30 in .45 and 24oz these can be had for around $500 or less. This gun does only give you a two finger grip but shoots surprisingly well. The Glock is fairly simple to operate just point and squeeze, but with all semi autos you have more moving parts along with magazines to keep track of.

My personal choice would be a revolver and the Ruger SP101 would be it. It is a 5 shot .357 at 25oz. It can be loaded with tamer .38s if needed. Very reliable and very easy to operate. You can carry it in a multitude of ways, my favorite being a cross-draw rig. While you do have some recoil the weight makes it manageable. And you can find them below $450.