I know people hate someone saying "I don't know they answer to your question but...", however that's exactly what I am doing - sorry!
No experience of the lens you are asking about, but a couple of close contenders. I have the 100mm f/2.8 L and absolutely love it. I consider it the best value for money L I own (and I do have a few). It is water resistant, has IS (in case that's important to you) and it is all in a remarkably tidy little package and tends to be cheap. It is reasonably fast, and you can happily shoot it wide open. It is a macro lens as well. You may be lucky and find a
second hand example for your budget, or save up for a bit longer. This is the lens which, if I were told I could only keep one, I would choose (from the, hmm, dozen lenses I think, never counted).
Then I also have the 135mm f/2 L. A very different lens, but also gorgeous in a different way. So fast, such lovely OOF highlights, such a slender DOF when wide open. Again it is not too large, although bigger than the 100mm. No IS or water resistance. As I say, a very different lens. You won't find a
second hand example at your budget (unless you are incredibly lucky), but if this is the lens that would suit you, get saving, it's worth it.
The classic portrait lens is the 85mm f/1.2 L, but in honesty, I could not recommend it. Sure it's very fast, and delivers wonderful results, but so expensive, so heavy, so large and so weird to use with the electronic focussing.
Good luck with your search.