Hello @heckflosse,
If you don’t need AF, go for a Apo-Rodagon lens.
Thanks. Never used the AF so far with my macro plants subjects 
As a plant pathologist, I mostly take pictures of fungi and bacteria samples.
When are savings are enough, I suppose I am going to opt for a macro lens in the 50-60 mm range. It is not necessary to have it internally stabilized because I always shoot with a tripod in our laboratory.