The 135L is a quite affordable lens (especially when bought used).
If you don't need AF there are a number of lenses faster than f/2.8 in the
range 135mm to 200mm ... some are already mentioned ... like to add one
here ... the Tamron SP 180mm f/2.5 (Adaptall-2 mount) ... not easy to get,
since there are not many of it around, but it offers excellent image quality.
Just a thought ... Rainer
If you don't need AF there are a number of lenses faster than f/2.8 in the
range 135mm to 200mm ... some are already mentioned ... like to add one
here ... the Tamron SP 180mm f/2.5 (Adaptall-2 mount) ... not easy to get,
since there are not many of it around, but it offers excellent image quality.
Just a thought ... Rainer