The going independent shop pice for a turn key valve job on the 103 is something in the area of $1,600 to $2,000. The machine shop labor and gaskets will probably run about $400 or so. This makes for pretty simple math.
For a competent DIY'er with adequate tools, I would call the R&R of head about a 16 hour job.
These engines come apart and go back together real well. You did need to be aware of a few basics such as tightening the rocker arm assemblies onto the cam gradually by tightening each cam stand a little then go to the next and so forth. If you just tighten one all the way then go to the next you will strip bolt holes and possibly break the cam.