If it were me, and I were trying to match a sub to those speakers on a budget, I would go with the Energy S10.3. It is a proven performer and very good for the price. My father in law has the same Klipsch speakers and they do not go very low at all. What that means is you will need a sub to fill in more of the mid range. Here is a quick example.
If you have speakers that will go down to 40hz, and you set the crossover on your receiver to, say, 60hz, the sub will handle everything below 60hz and your main speakers will do everything above 60hz (vocals, guitars, mid bass, etc. low bass and kick drums may be handled by the sub at this point). This is not exact, just an example. Mainly the "heavy lifting" is being done by the sub. Now say that your speakers only do down to 120hz (like the Klipsch sats you bought), your sub has to handle everything below 120hz (i.e. more midrange not just bass). Cheaper subs have a hard time with very low frequencies (LFE on movies) and upper mid bass can become boomy and muddy up the sound of your main speakers. Ideally you want speakers that go below 80hz (the standard THX crossover recommendation) because it is easier to blend the sub into the mix. If you want your setup to sound good, you are going to have to get a pretty good sub to fill in where those Klipschs are lacking. They will handle the highs fine, but you need something substantial to handle everything else. The Energy S10.3 is know to go deep enough and handle the mid range adequately.
If you are looking more at music usage over HT, a sealed sub tends to be a little tighter and punchier but doesn't did quite as deep for home theater.
Lava subs are known for having some nice mid range punch and wouldn't be bad either. The offerings from the big internet names on here (Hsu, SVS, Epik, Outlaw, etc) are probably going to be out of your price range.
Like I said, these are just examples. None of this is set in stone. There are many exceptions to what I have stated. Just some generalizations for you to consider.
We all have budgets and I totally understand that. If your budget is set, do some research and get the best bang for your buck. IMO, the nicer sub that you pair with those speakers, the much happier you will be.
Good luck in the search.