Very surprised by some of the previous comments - the Yashikor lens models, which formed the vast majority of the lettered Yashica models, are generally considered inferior to any model with a Yashinon. I thought that was a generally held belief. That is not to say that they are bad lenses per se, just that the Yashinon is generally regarded to have better performance. The bokeh of the Yashikor is very characteristic (in keeping with 3 element triplet style lenses), but the Yashinon's is generally cleaner and more uniform, as you'd expect from a better lens.
The late Yashica D's are basically very similar to the slightly newer Yashica Mats, but the Yashica Mat had a winding crank, and the D's used a slower winding knob.
The D couldn't have been a cut down on frills version of the 124G at all - the D came out in 1958, but the 124G didn't hit the market till 1970. It may look like that in terms of features, but that's purely because the older camera really was just older.
At that sort of budget, I wouldn't be too hung up on a light meter. The 124G meter is probably one of the better inbuilt meters on TLRs, seeing as the selenium cells in the more expensive Rolleiflex models tend to be broken, but TLR shopping is generally easier without the light meter prerequisite.