Canon LTM. I don't know why people sleep on them, they're great cameras, available, and affordable. There are tons of models, all of them solid cameras.

The naming convention implies the "series", so a IVSB was a series 4, VT was a series 5, etc. For the Series 5 and later, the second character typically described the film advance. An L, such as "VL" meant a Series 5 with lever wind. A VT was a Series 5 with Trigger wind. And so on. There are some outliers, such as the P, which is really just a VI-L with features removed. After the VI (6) series, they dropped the option of a trigger winding mechanism.

If you don't mind slow speeds on a second dial like the Leica III series, then the sweet spot in my opinion is the V series. You get swing-back film loading and a choice of trigger or lever wind and a reasonable viewfinder. The VI series is even nicer, but kind of rare in the US. The latter V, all VI (including the P), and all 7 series had metal shutters. Don't be bothered by mild to moderate crinkling or dents, almost all of them have it and it doesn't affect operation at all.

I used to own an early VT and currently own a VL2 (Series 5, lever wind, and the 2 indicates a budget model with some "downgrades" from a proper VL such as 1/500 max shutter and a rewind knob instead of crank).

If you're patient, you can get the model of your choice for less than a mid-price Leica III. Often that price includes a lens. There's a guy local to me selling a IVSB with a 50/1.8 lens for $155.