>
>Do you see EXISTS as potentially an alternative route here?

Quite possibly, yes.

One thing...on % cost for the execution operators....those are estimates and not exact values.

You might want to look at Time and IO statistics.

If you do this...

SET STATISTICS IO ON
SET STATISTICS TIME ON

And then run the query, in the messages area you'll get some good numbers to measure.

Any evaluation of execution operator cost %s should also be followed by an evaluation of the actual IO and time statistics.