I kind of agree with jackpine, and that is the approach I've taken. The answer to the seasons thing is to choose a gun you can conceal year round. A 10+1 9mm subcompact can be concealed in any clothing in my experience. Everyone is different though.
Back on topic, I think the Sig P220 Carry is the correct answer, but will also throw in the HK45c in LEM (no safety, constant action trigger, superior to strikers or DA/SA in my opinion). Both are going to be more expensive than $700, but anything else is a compromise. I've chosen not to compromise on carry guns, and over their lifetimes, I suspect I'll spend more on ammo and training than the firearms themselves, so I'm ok with it.
If under $700 is a must, look at the Beretta PX4 Storm in decocker-only variant. Given that criteria, I would personally probably get an M&P .45.