Most Porsche pundits, and even
Excellence magazine recommends that you purchase the newest Porsche you can afford.
Your cost cap gives you a lot of choices; and an affordable, low mileage 987 is one of them.
If you're that stressed about the IMS issue, you may want to consider one with a Certified Porsche warranty. Here's a very clean one below your cost cap:
Porsche Boxster Base Convertible 2 Door | eBay
Please note that this Boxster is being offered by a Porsche dealer, has less than 40K miles, and comes with a Certified Porsche warranty for two years or 50K miles. I believe this is different than a CPO, as my understanding is that Porsches more than 6 years old do not qualify for CPO status. If you pursue this, you may want to clarify with the dealer that the warranty covers an IMS failure.
Just a thought...........
TO