Is there a cassette checking device?
 

I know how to check my chain. I know my cassette is shot when a new chain doesn't help teh shifting.
That said, is there a way to actually check how near-worn-out a cassette actually is?

The darn Ultegra 10-speed cassettes are getting pricy. I'd like to use mine as long as possible, but not tooooo long.

Advice?

You, and I know this because I have found many, will be able to find innumerous 12-25 Ultegra 6700 cassettes for $35 on ebay or craigslist. Most of the ones I have seen are near new OEM parts that came on a bike equipped with a compact crank and were swapped out for an 11t.

Sure, it's called a "new chain". If it skips the cassette is junk.