As suggested, check the Bona Vacanta website, but do go back a couple of years if you find no recognisable surname on your first go.
Then, if you have not already done so I would make a stab at expanding your tree sideways so you have all distant Cousins, 2nd Cousins etc.
If you then still cannot make a connection go with the Heir Hunters but do negotiate fees.
I presume that you will have to provide certificates to show your valid relationship to the deceased and these could mount up to a fair amount which is why the Heir Hunters may be a reasonable option.