This isn't specific to halfings or clerics, but if you just want to find places to solo that are appropriate to your level you might want to check out the
Per-Level Hunting Guide.
It already has a couple of undead-only spots like Kaesora and the undead fort in Burning Woods that are perfect for clerics, but clearly it could use some more. If you find any please feel free to add them to the guide (or post them back here, or PM them to me and I'll add them).