There is a Red Mitchell "Mittel" set (I am assuming "Mittel" would be the proper designation, but I have never seen it referred to as such) and a weich set. There are also 4/4 and 3/4 variations. If you can get your hands on the 3/4 Mittel set, hypothetically it should feel more like a weich set would on a 41-42" string length.
As far as bass strings go, they're one of the cheaper options. You can usually find a set of them going for about $210 before sales tax, which might not be a problem depending on where you are located. They aren't in the same ballpark as some of the cheapest strings out there, but they have a crazy long lifespan. If this is something you seriously intend on pursuing, I'd say it's on the cheaper end of the double bass spectrum as far as prices go. If it's just an experiment, it's up to you if that's outside of your wallet's comfort zone.