I'll take a stab at this, although I am far from an expert. I have been hunting with muzzleloaders for over thirty years, but like you, they only interest me as an additional hunting opportunity.
How will you be hunting (treestand, still hunting, in the woods or over crops, etc.)? If extended range is a requirement, you need to look at rifles that are capable of an 150gr load.
I have never used Blackhorn 209, but it is my understanding that some rifles may require a modified breech plug to use it. I also understand that to get consistent ignition that the projectile has to fit the bore fairly tight, which means it will be harder to load.
All propellants have drawbacks. 777 pellets tend to leave a crud ring in the breech that makes bullet seating difficult if not brushed out after every shot. Both 777 & Pyrodex pellets have a short shelf life. Once you break the seal on the box you better figure on using it up that season. By next season you will be getting inconsistent ignition and velocities. Pyrodex and 777 are both hydroscopic and corrosive, even in unfired form.
After using pellets for several years, I'm back to using Pyrodex RS granular. If I could find a good supply of FFg black powder, I would use it instead of the Pyrodex.
What I look for is a rifle that is relatively light, has a decent trigger, and has an easily removable breech plug with 209 shotgun primer ignition. My hunting rarely offers shots over 100yds, so I'm not interested in long range capability.
I use a load of 80gr Pyrodex RS with a Hornady .430 265gr flat point bullet (the one for the .444 rifle cartridge) in a Harvester crush rib sabot. This combo loads easy in my current rifle and groups 3 shots consistently within 1-1/2" at 100yrds.
I haven't looked at any of the newer muzzleloaders recently, but you should be able to find something in the price range you're looking at. I would try a few and see what fits the best. Also, if you are looking to keep cost down, I wouldn't spend any extra on a stainless model, they will corrode almost as fast as CS if neglected.
