By "blue" you must mean the flat finish Rodeo. To me they're difficult to "behold" the 95% of the time it's not being shot, but makes a great platform for an antique job. That said, if you don't care about the cosmetics, it's got the same stellar innards of the glossier (CCH or pricier yet Pre War) ones. That's a vg price on the CCH one and in keeping with what another poster said, though their MSRP has gone (back) up this year...so grab one of those while you can! I've got the Colt as well with zero complaints, but can't argue the price of the USFA as you've found it. Caliber you'll hear all over the map. I lean toward (and have) a .44--just love the round and theoretical margin for "warming" it up reloading wise. I say theoretical as I don't presently reload. Others will extoll the virtues of the good 'ol .45 and hard to fault their choice either.
The .44 hasn't been catalogued for the Rodeo for a year or two..so if they have one (like I lucked into), it's gotta be NOS. Otherwise, I imagine their Rodeo selection is the standard .38 and .45 (USFA doesn't chamber a .357). The .44 Special is a regular offering in virtually all their other guns except "specialty" ones--Cavalries, etc--that weren't historically offered that way.
I had a .44-40 lever gun and loved it, but unless you're super into "old west" historical accuracy (vs the .44 Sp which was an early 20th Century invention), the .44 Special and .45 are more practical rounds to me--the former being able to be shot out of .44 Mag levers as well--with little niceties like snake shot available for them, and reloaders say easier, or at least more "conventionally" reloaded with their straight-wall and typically thicker cases.
Later Ed. - Unless I'm reading Davidson's pages and instant quotes wrong, of the ones they say are actually available, I only see a 7.5" among the .44 specials. For all around duty, I prefer shorter/handier. I'd say if you're going to get the CCH Single Action model, and if you "gotta have it now," get a 5.5" .45LC--and that's coming from a tried 'n true .44 guy! If you shoot ACP, later you can have a .45ACP cylinder fitted for more economical plinking. Of the Rodeos, hard to go wrong with a .45 (traditional) or .38 - low recoil (but capable of +Ps by the way) and cheaper shooting. I'd get a 5.5 in the .45 - just because - and a 4.75" in the .38, the latter to keep the weight down (littler holes) if no other reason.
You asked about ammo availability. This past year, everything's been very spotty. Otherwise, I've maybe seen more .44S (as the round has always been niche popular for SD as well as seein a resurgance in popularity - such as with the Lipseys Ruger BH/Flattop, or at least recognition),...then .45LC then .44-40. Can't say for the future. That's not to say there's been much of anything, including .38 Special.