The OC where I live had a similar request.
In our case the handrail was for 3 or 4 steps directly outside the requesting lot but in a common lobby area. The committee (I am the chair) decided to install it at OC expense. So the handrail become an asset to the common property.
As it turned out, other’s found it useful too!
If the handrail was to be installed in a lot property area or if it was only the requesting lot that would benefit from it, it might be fair enough for the requesting lot to pay for its installation.