Gary,
There's the rub, a custom caliber in a Ruger #1 requires custom gunsmithing. The rifle in question was custom barreled with a Douglas barrel some time ago and has been a "starter rifle" for several of us!
If I were looking for an off-the-shelf starter rifle, I would indeed look at the Ruger #1 in some "normal" caliber, such as their .375, which is a modern version of the .38-55. You might wish to go back and reexamine a couple of recent threads on gunsmiths and gunsmithing the #1. I might also look at Uberti or Pedersoli replicas of the high-wall Winchester in that same .38-55, and at the CPA Stevens copies of the Model 44 1/2 in whatever caliber fit my needs best.
Your question about multi-use suggests that maybe a single rifle to do all things is in your mind, be aware that multi-use means compromise. If you want to shoot BP cartridge events, I would maintain that anything under .38-55 will probably come up short for you, but then the big .40s can be downright brutal for long days of Schuetzen, so the .38 seems to fill in as an all-around caliber, not the very best at any one thing, but able to do a creditable job at a variety of things.
Finally, the word "inexpensive" means different things to different people. If your budget is in the $500 range, one of the tip-up rifles built on shotgun type actions may be the only thing available. In the $1000 range, we start seeing the rebarreled Rugers, Italian copies of 'walls, etc, and at about $2000 the selection broadens out considerably. "You pays your money..."
Whatever you decide, welcome to the wonderful world of single shots, and whatever you pick for a rifle, there will be other folks there that made the same choice and like it, and others who will be bound and determined to "convert" you to some other choice... that's just the way we are!
Regards,
Charlie Shaeff
the Green Frog